Summary of the FBI Laboratory’s Gunshot Residue Symposium,
May 31–June 3, 2005
Diana M. Wright
Michael A. Trimpe
Hamilton County Coroner’s Office
| Introduction | GSR
Defined | Composition
and Morphology | Hand
Sampling and Contamination | Case-Acceptance
Criteria | Testing
Victims and Suspected Suicides | Testing
Clothing | Instant
Shooter Identification Kits | Significance
and Report Writing | Technical
Review | Proficiency
Testing | Methodology
| ASTM Guidelines
| Conclusion | Editor's
Note | Acknowledgment
| References | Appendix
In response to the need for formalized gunshot residue (GSR) discussions,
the FBI Laboratory hosted a four-day symposium in the spring of
2005 to address a wide range of issues. Attendees included GSR examiners
and researchers from international, federal, state, and local government
agencies as well as private laboratories. The topics that were discussed
and the general guidelines that were approved by the group are presented
in detail. Some issues were too broad for the time allotted or will
require more study before consensus can be reached. Several participants
made plans to pursue some of these areas in greater detail, with
studies designed around suggestions initiated at the symposium.
There was agreement that the GSR community is in need of a document
that can provide general guidelines with respect to the policy for
accepting cases, the criteria necessary for reporting a positive
GSR result, and the importance of both elemental composition and
morphology in defining the presence of GSR.
In early 2005 approximately 40 scientists representing local,
state, federal, international, and private laboratories were invited
to attend an FBI-sponsored symposium dedicated to topics relevant
to the detection and significance of GSR analyses. This event was
held in Quantico, Virginia, from May 31 through June 3, 2005. The
mission of the symposium was to attempt to establish guidelines
for the acceptance, practices, and interpretation of GSR examinations
conducted primarily by scanning electron microscopy with energy
dispersive X-ray spectrometry detection (SEM/EDS). Although the
goals were ambitious, they were not unrealistic, given that the
attendees were selected based primarily on their experience level
and firsthand knowledge of key analytical aspects of the discipline.
Many of the symposium participants had previously conducted research
in selected areas that proved to be quite beneficial to the group.
These scientists shared their published and unpublished research
with the group in order to facilitate discussions.
From the early planning stages, the format of the symposium was
modeled after a scientific working group (SWG), in which experts
in the relevant area of discussion could present work that would
form the basis for discussion and eventual guidelines in that discipline.
In order to provide a starting platform for these discussions, several
topics of primary interest were sent to the attendees for review.
These topics were determined from discussions on a listserv dedicated
to forensic applications of SEM, as well as from discussions within
the general GSR/SEM community. Participants were encouraged to rank
the listed topics by importance and to add subjects that might be
more specific to the individuals or their agencies. This list formed
the basis for the order of the topics and the time allotted to each.
Participants were also surveyed regarding their level of expertise;
instrumentation; sample reports for positive, inconclusive, and
negative findings; and information pertaining to any legal challenges
they may have encountered in this discipline.
In order to encourage participation among the attendees, a consensus-building
format was established. Based on the ranked listings received during
the planning of the symposium, the moderator would open a topic
for discussion with a general statement such as, “A conclusion
regarding a positive GSR result should be based on both morphology
and elemental composition.” If the statement required clarification,
some discussion might ensue at that time. Once the statement was
in a form that was acceptable to most participants, a vote was taken.
The choices offered for a question such as described were usually
“Agree,” “Disagree,” or “Need to discuss
further.” The vote was conducted using a keypad system in
which all votes were recorded electronically and anonymously. The
tally was then projected onto a screen so that all attendees could
quickly determine if consensus had been reached. If a majority was
reached, the minority voters were allowed to comment further on
their vote or let the vote stand as it was decided. If the vote
was split, further discussion could be held to determine if the
discrepancy resulted from a poorly worded statement or a lack of
agreement as to the concept itself. Topics that were too broad or
deemed in need of additional study were set aside to allow for maximization
of the time allotted.
As a result of cumulative discussions, participants agreed upon some
general concepts, which will be shared in this paper. The discussions
that took place will provide a basis for more uniform agreement as
to how GSR evidence is accepted, analyzed, and interpreted. The symposium
participants agreed that more work is needed to establish criteria
in several key areas. However, progress was achieved in some areas,
and those discussions will be described here.
The first two topics were considered to be of primary importance
because they relate to the fundamentals of the examination. Participants
were asked if they could reach consensus as to the source of the
residue studied and the nomenclature used to describe it. There
was agreement that GSR originates in part from the firearm, the
cartridge case, and the bullet, with most of the inorganic residue
resulting from the primer. Most experts agreed that despite the
combination of potential sources that could contribute to the formation
of detectable residues, the best term to describe these particles
is gunshot residue, or GSR, as opposed to such
terms as primer residue or cartridge discharge residue.
When asked about terminology to describe the significance of GSR
particles, most experts said they prefer to describe the classic
three-component PbBaSb spheroid particle only as being characteristic
of gunshot residue rather than unique to
GSR. Only 4 out of 39 voting participants would choose to retain
the use of the word unique for such particles. (The majority
who chose to abstain from the unique classification cited
work by Torre et al. from 2002 that reported a rounded, molten non-GSR
particle that contained PbBaSb.) However, most attendees agreed
that when a population of particles is taken into consideration,
this type of three-component particle can be described as having
come from a discharged firearm. Particles containing only two of
the three components are currently described as commonly associated
with GSR, characteristic of GSR, consistent with
GSR, and/or indicative of GSR.
Additionally, the majority of attending experts stated that when
two-component particles are identified in the absence of three-component
particles, they would indicate the presence of these particles in
some form in their laboratory reports. Most of the experts also
agreed that BaSb particles no longer can be given the same weight
as PbBaSb particles because of the former’s reported presence
in some types of used brake pads. However, a majority of respondents
also indicated that it is possible to differentiate between brake
pad particles and gunshot residue particles. All agreed with this
statement when taking into consideration the entire population,
morphology, and elemental distribution in the particles. Studies
also have been conducted that find that similar conclusions can
be reached regarding fireworks (Mosher et al. 1998; Trimpe 2001).
Composition and Morphology
Almost all participants indicated that particle morphology, elemental
composition, and, if necessary, a comparison of any known residue
(from ammunition involved in the case) should be considered when
categorizing particles as GSR. All participants indicated that a
noncrystalline (nonsymmetrical) particle containing PbBaSb might
be characterized as a GSR particle. In conjunction with the elemental
profile, a majority indicated that the physical form of a GSR particle
should show evidence of rapid solidification in the form of a spheroid
or other shapes variously described as noncrystalline,
condensed, rounded, fused together, or
irregular. Sizes also would be expected to vary. There
was no definitive consensus reached as to what term would most likely
be used to describe the morphology of particles in residue from
a discharged firearm. However, the terms spheroid, condensed,
and rounded to describe particle shape were the most popular
from a list that also included noncrystalline, irregular,
molten, and none of the above.
To illustrate the importance of both morphology and elemental composition
in consideration of potential GSR particles, case studies of brake
pads were provided. Karl Lueftl and colleagues in Germany tested
brake pads from BMW vehicles and observed a small number of GSR-like
particles (with molten-looking shape), which lacked barium (Lueftl
and Gebhart 2004). A. J. “Skip” Schwoeble provided data
from 20 Volkswagen brake discs, from which he observed that all
potential GSR particles also contained Mg-Si-Fe constituents, thereby
disallowing a conclusion of positive firearm-related residues (Schwoeble
2005). John Giacalone’s study of brake pads supported this
work in concluding that GSR-like particles could be produced from
brake pads, but the exclusion based on nonallowed elements and the
morphology specifically associated with GSR make it possible to
distinguish between brake dust and firearm GSR (Giacalone 2000).
In a limited study conducted by the Texas Department of Public
Safety, 11 brake pads from automobiles in the laboratory’s
parking lot were sampled. A total of four SbBa particles were found
on the 11 sampling stubs. Of those four particles, one was composed
primarily of zirconium, one had a crystalline morphology, and the
remaining two were noncrystalline, nonspheroidal entities (White
2005). In another study to determine how often a three-component
GSR-like particle is found in brake dust, the Virginia Department
of Forensic Science completed a preliminary evaluation in 2004.
Brake dust samples were collected from 66 vehicles, including 8
Volkswagens and 2 Audis. More than 134,000 brake dust particles
were analyzed; 851 were classified as two-component particles during
the automated SEM/EDS analysis. The majority of those particles
were potentially barium sulfate. An occasional two-component BaSb
particle with high levels of iron was also detected. However, no
three-component (PbBaSb) particles were detected (DeGaetano, Maye,
and Harrison 2005).
A paper titled “Further Studies to Discriminate Primer Discharge
Residues from Particles of Environmental Origin” presented
at the 2005 SCANNING conference was also mentioned in the discussion
(Garafano et al. 2005). In this work, X-ray mapping revealed that
the PbBaSb distribution did not indicate a fusion of the elements,
but rather showed them to be only in proximity as nonhomogeneous
aggregates that appeared in dense fields of particles (i.e., not
separated far enough to prevent fluorescent excitation of elements
in nearby particles). Samples were obtained from 15 cars (11 models
of Volkswagen, Audi, Opel, and BMW manufacture) and 3 motorcycles
manufactured by Ducati. More than 100 particles were examined with
compositions similar to GSR (i.e., PbBaSb, BaSb, PbSb, or PbBa).
Results revealed that each of these particles was found with Pb
> Sb or Ba as reported by Torre et al. in 2002 and Cardinetti
in 2004. Fe, Cu, Zn, and Si, all “allowable” elements
in GSR residues, were also present in the spectra. The authors also
noted that particles of fused PbSb, which cannot be distinguished
from GSR species, were observed.
Hand Sampling and Contamination
All participants agreed that GSR sampling should be done at the
scene, where permissible, and as expeditiously as possible. With
respect to sampling and transfer concerns, it was unanimously agreed
that it would be best to sample a subject’s hands before bagging
the hands or placing the subject in a police vehicle. It was also
agreed that armed law enforcement officers can transfer GSR particles
to a subject through contact. Almost all participants agreed
that if the subject’s hands cannot be sampled before placing
the subject in a police vehicle, the subject’s hands should
be bagged in order to prevent possible contamination. Another recommendation
was that, to the extent possible, all used cartridge cases and/or
firearms be kept away from the GSR sampling kits, the area where
sampling will take place, and the area of the laboratory where GSR
analyses are performed.
The majority further agreed that it is possible for a handcuffed
person’s hands to be contaminated by the prior presence of
GSR in the backseat of a police vehicle. However, if asked in court
how likely it is for a handcuffed person’s hands to be contaminated
in the backseat of a police vehicle, most GSR experts would answer,
“I don’t know.” Faye Springer offered data from
a study of the backseats of law enforcement patrol vehicles in which
40 GSR samples were collected from 20 Sacramento Police Department
patrol units as the vehicles were returning from the officers’
shifts. None of the sampled backseats contained PbBaSb or PbBa particles.
However, 6 vehicles tested positive for lead particles, and 2 contained
one PbSb particle each (Springer 2005).
The Colorado Bureau of Investigation’s study of the backseats
of 26 law enforcement patrol vehicles indicated that at least 1
three-component particle was found in 14 of the vehicles. Five of
the remaining 12 vehicles had at least 1 two-component particle
detected. Only 7 vehicles had no PbBaSb particles detected (Rugh
and Crowe 2005).
Debra Kowal also provided data from a three-part study that attempted
to determine the occurrence of GSR in the law enforcement environment
(Kowal 2005). In the first part of the study, vehicles from half
of the Los Angeles County Sheriff’s substations were sampled
for GSR in the backseat “cupping area,” a well or cutout
in the lower portion of the seat where restrained individuals can
rest their hands during transport. Two-component particles were
detected on 45 of the 50 analyzed samples. Four of the 45 samples
also contained three-component PbBaSb particles. Only 5 of the 50
samples were negative for the presence of GSR particles.
Kowal conducted a second study with respect to the secondary transfer
of particles from the backseat of a patrol vehicle to a restrained
individual’s hands. A handcuffed person known to have GSR
on the hands was placed in the backseat of a patrol vehicle for
approximately 10 minutes, followed by a restrained individual known
to have hands free of GSR. Sampling of the second person’s
hands indicated that 12 three-component and 10 two-component particles
were transferred from the seat to the second individual’s
previously GSR-free hands.
The third part of the study described the transfer that took place
when an individual with “clean” hands was handcuffed
by an on-duty officer and placed in the backseat of a patrol vehicle
for 10 minutes. Of the 41 samples collected from the hands of the
previously “GSR-free” individuals, 20 had an average
of 5 two-component particles transferred from the law enforcement
environment (on-duty officer and/or patrol vehicle), 17 had no GSR-like
particle transfer, and 4 contained PbBaSb particles. In 3 of those
4 cases, the officers had qualified with their service weapons during
their shifts. The fourth transfer was noted on an individual who
was handcuffed by an officer who had last drawn his firearm in the
preceding 30 days.
In summary, the authors of the Kowal study demonstrated in the
first part that GSR is in the environment of patrol car backseats.
In part two, they demonstrated that transfer of GSR between a vehicle
backseat and an individual is possible. And in part three, results
indicated that GSR can be transferred from a law enforcement environment
to an individual’s hands. However, there are not sufficient
data to statistically calculate a rate of transfer.
Geoffrey Warman noted that contamination might be identified through
observation of the collective particle types and distribution observed
in the examined residue. His laboratory noted the presence of a
new particle type associated with pyrotechnic residues that was
found on armed law enforcement officers. These particles contained
Ba, Zr, Cr, Mn, with W also occasionally observed, and were concluded
to result from the use of flash-bang distraction grenades. Warman
concluded that these particles, if found on the subject, give independent
evidence of transfer occurring from armed officers (Warman 2005).
Michael Martinez reported on a study of 100 handcuffed subjects
who were sampled for the presence of GSR while in the custody of
local law enforcement officers. Sampling took place after transport
to magistrate court or jail while the subjects were awaiting arraignment.
Two-component particles (either PbBa or PbSb) were located on 16
percent of the subjects on their dominant, unwashed hands. None
of the subjects in this study had three-component particles on their
hands. The authors concluded that the particles were transferred
from a law enforcement officer, an inanimate object, or the back
of the law enforcement vehicle in which the subjects had been transported
(Martinez and Garcia 2005).
Another symposium participant offered information, which had been
shared previously on the Forensic SEM listserv, describing a contamination
study of different types of law enforcement vehicles, as well as
table surfaces and restraining bars in interrogation rooms. No three-component
(PbBaSb) particles were found in most of the sampled vehicles, although
two PbBaSb particles were detected in vehicles with cloth seats.
Table surfaces revealed a much higher rate of transferred PbBaSb
particles, reinforcing the need for sample collection prior to leaving
the scene. Thus, although the study determined that there is a chance
of secondary transfer to subjects from transporting or detaining
them, it was relatively low based on the collected data. That observation
was corroborated by the majority of the symposium participants.
Further discussion ensued as to how to resolve the issue of contamination
from contact between law enforcement personnel and subjects. Michael
McVicar provided preliminary data from a study conducted in Ontario
that was used to determine the prevalence of GSR on nonshooting
police officers. Sixteen volunteers for the study were sampled for
GSR on the backs of their left and right hands, the palms of their
shooting hands, the shirt sleeves on the side where they carried
their service firearms, the handles of their batons, and their handcuffs.
Slightly less than half of the officers had no three-component PbBaSb
particles on the surfaces tested. Four of the tested officers were
plainclothes detectives who tested positive for two-component BaSb
and three-component PbBaSb particles. A questionnaire the officers
filled out for the study did not indicate any activity that would
account for the presence of GSR (Randall and McVicar 2000).
Thus, although unlikely in practice, it was suggested by a large
majority of participants that in order to better distinguish between
GSR from contact with law enforcement versus a civilian shooting
event, a policy such as that set forth in some European Union countries
(e.g., Germany) should be set, which mandates that all domestic
law enforcement use ammunition with taggants detectable by SEM/EDS
(Niewoehner et al. 2005). This approach seems reasonable on a scientific
level because most experts further agreed that they do not know
of alternative methods to distinguish residue produced by police
It was widely agreed that the average person who is not exposed
to firearms or ammunition or its components will not be found to
have GSR particles on the hands. Michael Martinez conducted an occupational
study on 102 random individuals from 74 different occupations. The
individuals were residents from the community who had been called
for jury duty. Only one person was found to have a two-component
particle on his hands. This juror reported that he had cleaned his
hunting rifle 12 hours prior to being tested (Martinez 2005). These
results indicate that a subject’s daily environment can affect
the likelihood of finding GSR. James Garcia of the U.S. Army Crime
Laboratory reported that because the laboratory provides services
in conjunction with investigations of military personnel, it expects
to receive specimens with a higher propensity for elevated background
levels of GSR. Therefore, the Army Crime Laboratory requires a threshold
of at least four PbBaSb particles to report a positive GSR result
for these specimens. The threshold was instituted to allow for the
possibility of casual contact by subjects with firearms in the performance
of their duties. However, levels beyond this value would likely
involve greater exposure to GSR particles, namely, the recent discharge
of a firearm (Garcia 2005). The FBI Laboratory has established a
threshold for the number of GSR particles that is confirmed before
an item can be concluded to have been exposed to gunshot residue.
The number of particles used to confirm a GSR population is a minimum
of three PbBaSb particles. Additionally, other particles consistent
with a GSR-type environment also must be present: namely, SbBa,
BaPb, PbSb, and/or other elements or element composites routinely
found in GSR particle populations.
The majority of symposium participants overwhelmingly agreed that
particles can transfer from one surface to another and that bystanders
(e.g., a person present at the time of the shooting who does not
come into direct physical contact with the shooter, firearm, or
any other surface potentially contaminated with GSR) can test positive
for GSR. Michael McVicar also shared the results of a study that
sought to determine whether a bystander could be reasonably distinguished
from a shooter. The conclusion was that the high degree of variability
that exists in the deposition of GSR as a result of the ammunition-firearm
combination and the number of shots fired produces an overlap between
the GSR concentrations obtained from sampling either a shooter or
bystander as quickly as 15 minutes postfiring. Therefore, the number
of particles cannot be used as a basis for determining if someone
fired, or was merely in the vicinity of, a recently discharged firearm
(Lindsay and McVicar 2004).
Symposium participants also discussed that given the ease of transfer
of GSR between surfaces, routine monitoring of the work environment
should be included in a laboratory’s standard protocol for
GSR testing. At least 31 of the participants currently perform some
form of routine testing in their laboratories to determine whether
contamination is present.
Michael Martinez described an ongoing study his laboratory is conducting
in an attempt to identify any GSR-positive “hot zones”
within laboratory space. The results to date have led to a policy
that no GSR examiner may enter the GSR instrument room on a day
in which prior contact has transpired with any area of the firearms
section of the laboratory (Martinez 2005). Michael McVicar stated
that the policy of his laboratory restricts access such that no
person who has handled a firearm or ammunition component, sampled
an item for GSR, or entered the firearms section of the laboratory
may enter the SEM laboratory for the remainder of that workday.
Ludwig Niewoehner mentioned work that has been presented regarding
the use of a clean room to cut down on the number of contamination-control
samples that need to be run to ensure a GSR-free environment (Niewoehner
and Neimke 1999). Wayne Niemeyer presented similar work regarding
contamination studies and the use of a clean room (Niemeyer 2005).
Before discussing acceptance criteria, the participants agreed
that the most probative value of GSR examination occurs in cases
where the subject claims to have not handled or fired a firearm.
The great majority of participants agreed that there is no value
in collecting separate samples from the back and palm surfaces of
the hand because it is more misleading than informative. Furthermore,
the analyst should have the discretion to prioritize the samples
submitted and discontinue the analysis when GSR is found. The participants
also agreed unanimously that it is appropriate for a laboratory
to have acceptance criteria or to limit the number of items examined.
Symposium participants also discussed time limits between a shooting
incident and the collection of GSR on live subjects. Many participants
stated that an acceptable cutoff time is 4 to 6 hours after the
shooting event, whereas some felt that up to 8 hours was appropriate.
Still others were comfortable accepting lifts taken more than 12
hours after the shooting. The Virginia Department of Forensic Science
recommends sample collection within 4 to 6 hours of the shooting
event as long as the hands have not been washed. Geoffrey Warman
from England’s Forensic Science Service commented that subjects
could recontaminate their hands up to the time of arrest and that
there was no probative value in examining samples taken more than
4 to 6 hours after arrest. He further noted that findings in relation
to samples taken many hours after a shooting are better attributed
to a more recent event or the redistribution of particles from some
other contaminated surface (Warman 2005). For its acceptance policy,
the FBI Laboratory uses a cutoff of 5 hours. The Florida Department
of Law Enforcement and the Centre of Forensic Sciences in Toronto,
Ontario, Canada, both have a stated time limit not to exceed 8 hours
(Radcliffe 2005; McVicar 2005). All of the attendees stated that
they recommend that samples be collected from the hands as quickly
as possible and that laboratories may elect not to analyze lifts
from the hands of live subjects 4 to 12 hours after the event in
Some of the attending laboratories also have policies in place
to exclude analysis of samples collected from victims of gunshot
wounds or anyone known to have handled a firearm. Many laboratories
accept samples from only the hands, as opposed to other areas of
the body, such as the face. This policy is supported by data presented
by Douglas DeGaetano from Virginia. In an 18-month study conducted
between 1993 and 1994, he reported that of 286 face samples analyzed,
GSR was found on the face in only 9 cases in which the hand samples
were negative (DeGaetano 2005). Only one-quarter of the participants
at the symposium receive GSR lifts collected from the face of a
subject. An overwhelming majority of the participants would consider
analyzing face samples but agreed they should be examined only if
hand samples are negative or unavailable.
When asked if it is satisfactory to use a single stub for sampling
both hands and face together as long as tackiness remains, the majority
disagreed. One of the concerns cited was the potential for high
numbers of cosmetic particles—including bismuth, titanium,
and iron-based pigments—on the facial area. These particles
can hinder the search for GSR. Keeping the face and hand samples
separate alleviates concerns about masking GSR particles on the
hands with contaminants from the face. When asked if it is satisfactory
to use one stub for sampling both hands together as long as tackiness
remains, two-thirds agreed. However, one participant voiced the
opinion that sometimes circumstances dictate the use of multiple
stubs and that valuable information could be lost if those samples
are not collected.
The types of kits that the participating laboratories will accept
vary. Some participants stated that they accept “two lifter”
kits, some accept “four lifter” kits, and the majority
stated that they will accept any type of SEM/EDS GSR kit they receive.
It was suggested that when in doubt, if the laboratory did not supply
the kits to the contributor, it is wise for the contributor to phone
the laboratory prior to sample collection for clarification about
Under the subject of acceptance criteria, the participants were
asked if they perform quality assurance (QA) testing on their supplier’s
GSR kits before using them in the field. Less than half test the
kits themselves, and most are satisfied with the supplier’s
QA testing assurances.
About half of the participants require that the information sheet
with the kits have certain mandatory information filled out before
they will accept the kit. Many have no such requirements, and only
a few require that the sheet be filled out completely.
and Suspected Suicides
When asked if GSR testing should be done on suspected suicide
victims, almost all participants agreed that these samples should
be collected; however, they should be analyzed only if probative
value can be shown.
The overwhelming majority of the experts agreed with the following
- Analyzing lifter samples for GSR from victims can never prove
whether the subject is a victim of a suicide, a homicide, or an
- Particles are expected to be found on a victim shot at close
range or within a reasonable distance from the muzzle, up to several
- Depending on the circumstances, some victims near the shooting
may not have GSR particles on them.
In these discussions, Douglas DeGaetano reported that in a 10-year
study of 5,231 GSR-related cases in Virginia, 39 percent (2,040
cases) involved possible suicides. Of this number, roughly 13 percent
of suicide victims did not test positive for GSR particles. GSR
collected from the hands of suicide victims at the scene was positive
92 percent of the time, whereas GSR collected from the hands of
suicide victims at the morgue was positive 76 percent of the time
(DeGaetano and Harrison 2004).
Michael Trimpe conducted a two-year study at the Hamilton County
Coroner’s Office (Ohio) during which 80 victims of suspected
suicide were sampled for the presence of GSR. Seventy-nine percent
of the victims tested positive for either two- or three-component
classic GSR particles. Some of the reasons hypothesized for a negative
result on 21 percent of the victims tested included medical attention
received prior to sampling, bagging of the hands, time delay between
the shooting and sampling and subsequent transport of the body,
weather conditions, weapon type, number of shots fired, and refrigeration
of the body prior to sampling for GSR. In the last scenario, condensation
on the skin could remove GSR particles prior to sampling, much as
hand washing or heavy perspiration might (Trimpe 1997).
A similar study was conducted by Michael Martinez in Bexar County,
Texas, on 126 suspected suicide victims involving at least five
different calibers of weapon. Only 48 of the individuals sampled
tested positive for GSR. Of this number, 10 percent had only one
GSR particle present. Possible reasons for the results included
large amounts of blood on the surfaces sampled, a new or cleaned
firearm used in the shooting event, an incorrect cause of death
reported by medical examiners, and improper sample collection. It
was concluded that if further testing was desired, the weapon and
ammunition should be submitted (Martinez and Garcia 2005).
Finally, Carol Crowe reported that the Colorado Bureau of Investigation
keeps a database to track the rate of positively confirmed GSR on
victims of fatal gunshot wounds. Current information revealed that
the bureau has classified GSR on 80 percent of homicide victims
(94 out of 118 people with at least one PbBaSb particle found) versus
a rate of 94 percent for victims of suicide (156 out of 166 people
confirmed to have at least one PbBaSb particle on the area sampled)
Discussions confirmed that the presence of GSR cannot determine
whether the victim’s death was the result of a homicide or
a suicide; moreover, some suicide victims can test negative for
the presence of GSR depending upon the circumstances and environmental
conditions imposed postmortem on the body prior to sampling.
Discussions were also held regarding testing clothing for the
presence of gunshot residues. Attendees who have performed research
or casework in this area provided details for reference. The sampling
technique and materials were described as analogous to hand sampling
in an article that originally appeared in the IAMA Newsletter
(International Association for Microanalysis) (Martinez 2000).
Guidelines for sample submission and acceptance were offered by
Michael McVicar (McVicar 2005). These parameters included collecting
the sample at the laboratory by trained personnel who have not discharged
or been in the vicinity of a discharged weapon within the past 24
hours prior to sample collection. If personnel seizing the clothing
have discharged a weapon, at a minimum, they should thoroughly wash
their hands, change their clothes, and don gloves prior to evidence
collection. With respect to packaging the clothing, paper (bags
or wrapping), rather than plastic, is recommended. Additionally,
larger garments should be folded with brown paper between the folds
in order to prevent the transfer of GSR from one area to another.
If the latter step is not taken, it is recommended that the analyst
photograph the clothing in its packaging as received to demonstrate
why a conclusion cannot be reached as to where the particles originated
on the garment. A. J. Schwoeble of the RJ Lee Group in Pennsylvania
suggested the use of white “butcher-type” waxed paper
as an alternative to the traditional brown kraft paper in order
to prevent the introduction of fibers from the paper onto the garment
With respect to case acceptance of clothing items, Michael McVicar
advised that the Centre of Forensic Sciences also instructs its
contributors to ensure that the garment being submitted can reasonably
be expected to have had direct contact with or proximity to a discharged
firearm. Within this context, a shirt worn inside another layer
would not be as probative for sampling purposes as the outer garment.
Other items such as shoes would similarly be considered too far
removed from the discharge to have received appreciable amounts
of residue. Finally, items with a surface relatively free of loose
debris or easily shed fibers are preferable.
Carol Crowe provided a study performed by the Colorado Bureau of
Investigation in which clothing was tested for GSR residues subsequent
to discharging a weapon and laundering the worn garments in a conventional
washing machine with warm water and detergent (Chavez et al. 2001).
A variety of garments and fabrics were tested both postfiring and
postlaundering. Results demonstrated the persistence of three-component
GSR particles and/or two-component (supporting) particles on some
of the garments even after washing. However, as the authors stated
in their conclusions, the presence of GSR on clothing cannot provide
confirmation of a recent association with a discharged firearm in
the same manner that such findings on a living person’s skin
(i.e., hands or face) might suggest. In other words, time of GSR
deposition on clothing cannot be assessed in the same context as
when it is confirmed on specimens taken directly from skin surfaces.
Several participants offered evidence that persistence on fibrous
materials is longer than on skin. In particular, a study by A. J.
Schwoeble found that the number of PbBaSb particles discovered after
clothing was laundered was reduced between 88 and 99 percent. Thus,
whereas most PbBaSb particles were found to be in the 1–10-µm
size range before washing, only particles less than 2 µm were
Other suggestions provided for the analysis of clothing included:
- Sampling the clothing while it is still worn by the subject
rather than packaging it for transport to the laboratory.
- Carbon-coating all stubs used to sample fibrous material to
reduce or prevent charging effects.
- Dedicating the SEM chamber to only one case when fibrous samples
are being analyzed, in the event of particle transfer from charging
- Using adhesive lifters, which are better suited to GSR examinations
of clothing surfaces than vacuuming all matter embedded in the
fabric weave, when attempting to locate GSR particles from a recent
- Sampling areas on the garment where a weapon could be concealed
(e.g., pocket interiors).
In conclusion, the participants unanimously agreed that there
are circumstances when items of clothing associated with a subject
and event should be examined for the presence of GSR (e.g., when
hand samples are negative or not available).
Shooter" Identification Kits
With respect to combination kits, such as field-use “instant
shooter kits” (marketed as ISID, RIFF, or other brands), GSR
lifts for SEM should always be taken before the instant shooter
swabbing is employed. Unequivocally, taping (using adhesive lifts),
as opposed to swabbing, for GSR by SEM is the best form of sampling.
The marketed instant shooter kits are essentially an updated version
of the dermal nitrate test that uses a color change to detect the
presence of nitrates.
Historically, the dermal nitrate test has been shown to produce
many false positives and is not specific for the presence of GSR.
The use of the presumptive kits now being marketed may cause the
loss of GSR particles. Of the kits marketed for rapid detection
of nitrates (presumably from nitrocellulose in smokeless powder),
extraction procedures are cumbersome, time-consuming, and much less
successful at recovering GSR particles than adhesive lifts. This
finding was reported by Faye Springer in a recent journal article
(Hanson and Springer 2005) and has been independently corroborated
at the FBI Laboratory. As a result of discussions among attendees
from several laboratories that have observed similar problems, the
majority of the group members did not think these kits should be
used to collect or test for GSR in place of SEM/EDS analysis, and
most were not willing to analyze them for this purpose. Moreover,
although there was no strenuous objection to independent laboratories’
performing further tests on instant shooter kits for GSR particle
retention, some participants advised against it for the reasons
With respect to the significance of the results obtained, most
experts felt that even one PbBaSb spheroid particle is enough for
a “positive” result. However, almost all of the attending
experts agreed that GSR particles alone cannot be attributed to
a particular shooting event. It also cannot be determined what actually
occurred with respect to a shooter’s hands between the time
of shooting and sampling. It is understood that GSR particles cannot
be used to distinguish between shooters and bystanders. Similarly,
the absence of gunshot residues on a sample does not preclude the
possibility of that individual’s having discharged a firearm.
Many of the experts also stated that these caveats are included
in some form in reporting out inconclusive or negative results.
Along the lines of interpretation, some experts stated that they
list particle counts to report everything found in a search for
GSR, whereas others felt that this approach might be misleading
to those who are unable to interpret results. More than half of
the respondents indicated that the use of particle counts needed
to be followed by an opinion statement to provide context to the
A majority of the attendees reiterated throughout these discussions
that a qualifying statement is needed in reports. The following
example is considered an appropriate qualifying statement to use
when particles are found on a person’s hands: the findings
are “consistent with that person’s having fired a weapon,
having been in the vicinity of a fired weapon, or having touched
an item with gunshot residue on it.” For negative results,
GSR may not have been detected for reasons that may include:
- Lack of exposure of the individual to GSR.
- Removal of particles through physical activity, hand washing,
or weather conditions.
- Lack of traditional GSR components in the ammunition (e.g.,
organic primer formulations or primers lacking one of the three
components associated with GSR).
- Heavy soil deposition on the surface being sampled.
- Improper use of the collection kit (e.g., rubbing the sampling
surface with the stub rather than dabbing might cause damage to
the tape surface).
- Lack of deposition of an acceptable threshold of GSR particles
by the discharged firearm.
Depending on the request, other qualifiers might also be used
to convey limitations. Examples include the inability of GSR examinations
to determine firing angles, the handedness of the shooter, the hand
used to discharge the weapon, and the type of weapon used.
Many of the responding attendees agreed that it is good practice
to compare residue found on the suspect to the shooting event through
examination of the firearm, spent ammunition from the scene, or
the victims’ clothing; however, it is not essential to do
so. Similarly, slightly more than half agreed that the firearm should
be test-fired, when available and applicable in a GSR case, to determine
if residues are deposited. It is generally acknowledged that residues
released from ammunition during discharge are not all generated
from that shooting event (Schwoeble and Exline 2000). Rather, the
residue population may also include contributions from ammunitions
previously fired from that gun. Therefore, the direct comparison
of residue populations from the victim, suspect, and test firings
must be interpreted with caution.
The majority of attendees indicated that their laboratories require
that all GSR reports be peer-reviewed (i.e., technically
reviewed) prior to being released and that they support this policy.
The majority agreed that, at a minimum, the American Society of
Crime Laboratory Directors/Laboratory Accreditation Board (ASCLD/LAB),
or some other relevant accrediting body, should set a policy as
to what percentage of all reports should be peer-reviewed (technically
reviewed) by another qualified examiner prior to release.
Some symposium participants work for laboratory systems that do not
have a policy for any technical review prior to issuing a report.
However, most of the attendees agreed that an administrative review
alone is not sufficient to ensure technical accuracy. Further discussion
elucidated the idea that the time spent in review is helpful to both
the reporting examiner and the reviewer with respect to sharing ideas
and minimizing testifying to a report with inaccuracies ranging from
typographical errors to technical mistakes.
With respect to quality-assurance-related topics, the symposium
participants all agreed that the European Network of Forensic Science
Institutes’ (ENFSI) GSR proficiency test should be adopted
as an approved test for GSR analysis by SEM/EDS (Niewoehner et al.
2005). This standard sample, prepared by the PLANO Company in Germany
in accordance with ISO (International Organization for Standardization)
5725 for the performance of proficiency tests, consists of “synthetic
GSR particles” with the composition of PbBaSb precipitated
onto a silicon substrate previously coated with a carbon layer.
Although it is not a good representation of a real-world GSR sample,
it is the best proficiency-testing sample currently available for
GSR. It can also be used for system validation.
Most experts also agreed that they would be willing to participate
in a round-robin proficiency test in the absence of a standardized
commercial GSR testing program. Roughly half of the respondents
agreed that they would even participate in a round-robin to the
extent that they would accept responsibility for preparing and distributing
the test on a rotating basis.
The majority also agreed that examiners who perform GSR analysis
should be proficiency-tested specifically in GSR regardless of whether
they have already been tested on other materials characterized as
Finally, the majority of participants agreed that they look for
submicron particles in their automated search routines, and therefore,
neither a specific test for proficiency nor an instrument vendor
should dictate what range of particle sizes should be characterized
or studied in an analysis.
The symposium attendees stated that, in general, they conduct
GSR analyses using SEM/EDS. Although the vast majority confirmed
that they perform these examinations using automated search routines,
the group unanimously agreed that manual confirmation should always
be performed for at least a representative sample of the population.
It was stated unequivocally that automated search routines alone
cannot be used reliably to report a positive GSR result.
With the development of test methods that identify multiple components
of smokeless powder and its additives rather than only nitrate residues,
the group supported participation in research and development in
this area. Particular mention was made regarding research into organic
residues. New technology recently acquired by two laboratories whose
personnel attended the symposium may hold promise in this regard.
The instrument of interest is a time-of-flight mass spectrometer
capable of real-time, nondestructive analysis of a wide range of
materials commonly encountered in forensics. It is expected that
research into its applicability to non-lead- based GSR residues
will be forthcoming in the literature.
Further discussion and research was also advocated in the area
of primers that produce nonclassical GSR residues, such as BaSbAl
or TiZn or other non-lead-containing components. Time constraints
limited the scope of this topic, and as a result, no definitive
statements were offered for consensus voting. However, the area
remains one of interest within the community and does warrant future
A representative from ASTM International was present at the symposium
to provide the attendees with an update as to the progress made
to date on the ASTM guide E1588-95(2001) Standard Guide for
Gunshot Residue Analysis by Scanning Electron Microscopy/Energy-Dispersive
Spectroscopy. The group was given an overview of the status
of the revision of the guide and encouraged to discuss any problems
with the current ASTM guideline. Comments and suggestions were noted
for later discussion within the committee.
At the conclusion of the symposium, several topics remained open
for further discussion: namely, the use of time limits in case-acceptance
criteria and how to standardize the language used to report the
presence of GSR particles. Topics such as these are often dictated
by individual laboratory policies, as well as the circumstances
of a particular case. Therefore, it is unlikely that universal guidelines
and terminology will evolve for the GSR community in these areas.
Some important topics were not discussed because of time limitations,
specifically, airborne particles and elemental contributions from
different ammunitions. However, the limitations of GSR examinations
were unanimously recognized, such that the use of qualifying statements
in report writing and testimony was discussed in detail. It is expected
that the language of qualifiers will continue to develop in order
to provide juries with a sound basis to evaluate the conclusions
reached through GSR analyses. Research is also continuing in the
areas of retention and contamination or transfer. It is hoped that
these studies will be more readily available to the GSR community
in the future through the use of Internet listservs and forums such
as this one.
The FBI recently decided to stop conducting GSR examinations.
This decision was made after an internal assessment of the number
of requests received for this examination in recent years and the
probative nature of those requests.
The FBI Laboratory continues to believe that the GSR examination
is valuable but has decided to use the resources previously dedicated
to GSR in areas directly related to fighting terrorism, which is
the FBI’s primary mission.
The FBI Laboratory stands behind the reports it has already issued
using this technique. Should a future case require GSR analysis,
the Laboratory will send to the requesting agency a list of state,
local, and private laboratories that conduct GSR examinations.
This is publication number 06-03 of the Laboratory Division of
the Federal Bureau of Investigation. Names of commercial manufacturers
are provided for identification purposes only, and inclusion does
not imply endorsement by the FBI.
Cardinetti, B. X-Ray Mapping Technique: Gunshot Residue Particles
vs. Aggregates from Environmental Origin. Presented at SCANNING,
Washington, D.C., 2004.
Chavez, D., Crowe, C., and Franco, L. The retention of gunshot
residue on clothing after laundering. IAMA Newsletter
Crowe, C. Colorado Bureau of Investigation, personal communication
at the FBI Laboratory GSR Symposium, May 31–June 3, 2005.
DeGaetano, D. H. Virginia Department of Forensic Science, personal
communication at the FBI Laboratory GSR Symposium, May 31–June
DeGaetano, D. H. and Harrison, L. G. GSR by SEM/EDX at the
Commonwealth of Virginia—Ten Years of Data from Spreadsheet
to Database. Presented at SCANNING, Washington, D.C., 2004.
DeGaetano, D. H., Maye, S., and Harrison, L. G. Virginia Department
of Forensic Science, personal communication at the FBI Laboratory
GSR Symposium, May 31–June 3, 2005.
Garafano, L., Fratini, P., Minardi, M., Bizzaro, G. P., Tortora,
F., and Manna, L. Further Studies to Discriminate Primer Discharge
Residues from Particles of Environmental Origin. Presented
at SCANNING, Monterrey, California, 2005.
Garcia J. D. U.S. Army Crime Laboratory, personal communication
at the FBI Laboratory GSR Symposium, May 31–June 3, 2005.
Giacalone, J. Putting the Brakes on Gunshot Residue. Presented
at SCANNING, San Antonio, Texas, 2000.
Hanson, A. M. and Springer, F. A. An evaluation of Instant Shooter
Identification (ISid™) gunshot residue kits, AFTE Journal
Kowal, D. Gunshot Residue in the Law Enforcement Environment.
Presented at the California Association of Criminalists meeting,
Glendale, California, 2000.
Lueftl, K. and Gebhart, E. GSR-Like Particles from Brake Pads.
Presented at the BKA GSR Symposium, Bad Camberg, Germany, 2004.
Lindsay, E. and McVicar, M. J. Passive Exposure and Persistence
of Gunshot Residue on Bystanders to a Shooting: Can a Bystander
Be Differentiated from a Shooter Based on GSR? Presented at
the joint meeting of the Canadian Society of Forensic Science and
the Southern Association of Forensic Science, Mid-Atlantic Association
of Forensic Science, and Midwestern Association of Forensic Science,
Orlando, Florida, 2004.
Martinez , M. V. Bexar County Criminal Investigation Laboratory,
personal communication at the FBI Laboratory GSR Symposium, May
31–June 3, 2005.
Martinez , M. V. P-GSR detection on clothing and in automobiles,
IAMA Newsletter (2000) 1(2):2–3.
Martinez , M. V. Bexar County Criminal Investigation Laboratory,
and Garcia J. D. U.S. Army Crime Laboratory, personal communication
at the FBI Laboratory GSR Symposium, May 31–June 3, 2005.
McVicar, M. J. Centre of Forensic Sciences, Toronto, Ontario, Canada,
personal communication at the FBI Laboratory GSR Symposium, May
31–June 3, 2005.
Mosher, P. V., McVicar M. J., Randall E. D., and Sild, E. H. Gunshot
residue-similar particles produced by fireworks, Canadian Society
of Forensic Science Journal (1998) 31(2):157–168.
Niemeyer, W. D. McCrone Associates, Inc., Westmont, Illinois, personal
communication at the FBI Laboratory GSR Symposium, May 31–June
Niewoehner, L., Andrasko, J., Biegstraaten, J., Gunaratnam, L.,
Steffen, S., and Uhlig, S. Maintenance of the ENFSI proficiency
test program on identification of GSR by SEM/EDX (GSR2003), Journal
of Forensic Sciences (2005) 50:877–882.
Niewoehner, L. and Neimke, D. Establishing a Cleanroom for
GSR Investigation—A Necessity or Not? Presented at the
ENFSI EWG meeting, Den Haag, The Netherlands, 1999.
Radcliffe, D. T. Florida Department of Law Enforcement, personal
communication at the FBI Laboratory GSR Symposium, May 31–June
Randall, D. and McVicar, M. J. A Study to Determine the Prevalence
of GSR on Non-Shooting Police Officers. Preliminary results
presented at the 47th Canadian Society of Forensic Science meeting,
Ottawa, Ontario, Canada, November 2000.
Rugh, A. and Crowe, C. The Prevalence of Gunshot Residue in
Law Enforcement Patrol Cars. Presented at SCANNING, Monterey,
Schwoeble, A. J. GSR Persistence on Clothing. Presented
(poster form) at the 51st American Academy of Forensic Sciences
meeting, Orlando, Florida, 1999. Also presented (oral format) at
the 26th Mid-Atlantic Association of Forensic Scientists meeting,
Ocean City, Maryland, April 21–23, 1999.
Schwoeble, A. J. RJ Lee Group, Monroeville, Pennsylvania, personal
communication at the FBI Laboratory GSR Symposium, May 31–June
Schwoeble, A. J. and Exline D. L. Current Methods in Forensic
Gunshot Residue Analysis. CRC Press, Boca Raton, Florida, 2000,
Springer, F. A. Sacramento County Office of the District Attorney
Laboratory of Forensic Services, personal communication at the FBI
Laboratory GSR Symposium, May 31–June 3, 2005.
Torre, C., Mattutino, G., Vasino, V., and Robino, C. Brake linings:
A source of non-GSR particles containing lead, barium, and antimony,
Journal of Forensic Sciences (2002) 47:494–504.
Trimpe, M. A. A Review of Gunshot Residue Test Results in 80
Suicide Cases. Presented at the American Academy of Forensic
Sciences meeting, New York, 1997.
Trimpe, M. A. Analysis of Fireworks for Particles of the Type
Found in Primer Residue (GSR). Presented at the American Academy
of Forensic Sciences meeting, Seattle, Washington, 2001.
Warman, G. Forensic Science Service, London, England, personal
communication at the FBI Laboratory GSR Symposium, May 31–June
White, T. R. Texas Department of Public Safety Crime Laboratory
Service, personal communication at the FBI Laboratory GSR Symposium,
May 31–June 3, 2005.
The following scientists participated in the 2005 FBI Laboratory
Robert Berk, Illinois State Police, Chicago, Illinois
JoAnn Buscaglia, FBI Laboratory, Quantico, Virginia
James Crippin, Western Forensic Law Enforcement Training Center,
Carol M. Crowe, Colorado Bureau of Investigation, Lakewood, Colorado
Douglas H. DeGaetano, Commonwealth of Virginia, Department of Forensic
Science, Richmond, Virginia
John E. Drugan, Massachusetts State Police Crime Laboratory, Sudbury,
Patricia C. Eddings, Tarrant County Medical Examiner’s District
Crime Laboratory, Fort Worth, Texas
Gamal Emira, Philadelphia Police Department Forensic Science Center,
James D. Garcia, U.S. Army Criminal Investigation Laboratory, Forest
John R. Giacalone, State of Alaska, Department of Public Safety,
Lawrence Gunaratnam, National Bureau of Investigation Crime Laboratory,
Joseph Harant, Baltimore City Police Department Laboratory, Baltimore,
Annalivia Harris, Montana State Crime Laboratory, Missoula, Montana
Robert L. Hinkley, Alameda County Sheriff’s Office Criminalistics
Laboratory, San Leandro, California
James L. Jackson Jr., Harris County Medical Examiner’s Office,
Robert D. Koons, FBI Laboratory, Quantico, Virginia
Debra Kowal, Los Angeles County Department of Coroner, Los Angeles,
Thomas A. Kubic, TAKA, Inc., Northport, New York
Jozef Lebiedzik, Advanced Research Instruments Corporation, Golden,
Karl Lueftl, Bayerisches Landeskriminalamt (Bavarian State Criminal
Police Agency), Munich, Germany
Michael Martinez, Bexar County Criminal Investigation Laboratory,
San Antonio, Texas
Deborah Messina, Connecticut State Forensic Science Laboratory,
Michael J. McVicar, Centre of Forensic Sciences, Toronto, Ontario,
Wayne D. Niemeyer, McCrone Associates, Inc., Westmont, Illinois
Ludwig Niewöhner, Bundeskriminalamt (BKA, Federal Criminal
Police Office), Wiesbaden, Germany
Laila (Benham) Parahinia, Santa Clara County District Attorney’s
Crime Laboratory, San Jose, California
Elizabeth Patel, North Carolina State Bureau of Investigation,
Raleigh, North Carolina
Michael Platek, Rhode Island State Crime Laboratory, Kingston,
Koren Powers, West Virginia State Police Forensic Laboratory, South
Charleston, West Virginia
Daniel T. Radcliffe, Florida Department of Law Enforcement, Daytona
Sandra B. Sachs, Office of the Chief Medical Examiner, San Francisco,
A. J. Skip Schwoeble, RJ Lee Group, Inc., Monroeville,
Ila Simmons, South Carolina Law Enforcement Division, Columbia,
Jenny Smith, Missouri State Highway Patrol Forensic Laboratory,
Jefferson City, Missouri
David W. Spence, Southwestern Institute of Forensic Crime Laboratory
Services, Dallas, Texas
Faye Springer, Sacramento County District Attorney, Sacramento,
James N. Stam, San Diego Police Department, San Diego, California
Michael A. Trimpe, Hamilton County Coroner’s Office, Cincinnati,
Dennis C. Ward, FBI Laboratory, Quantico, Virginia
Geoffrey Warman, Forensic Science Service, London, England
Robert S. White, Legal Science, Charleston, West Virginia
Thomas R. White, Texas Department of Public Safety Crime Laboratory
Service, Austin, Texas
Diana M. Wright, FBI Laboratory, Quantico, Virginia