How long does it take for a gunshot Residue test to take?
Over the past several years, research and technology have brought about changes to the GSR examination.The Final Report on Particle Analysis for Gunshot Residue Detection was released in 1977 and still stands as an excellent comprehensive report on the analysis and interpretation of primer GSR.Recent technological advances have made particle analysis quicker and easier, but most current research involves the interpretation of results.
Increased understanding and increased confidence in GSR interpretation have been brought about by improved communication among gunshot residue analysts.Reputable scientists always have reported that the finding of GSR cannot indicate the shooter, yet members of the media usually don't.Many population studies have shown that GSR isn't usually found on the average person, which adds value to the findings.
A discussion of the collection, analysis, interpretation, and reporting of GSR requires an understanding of primer residue particles.Most gunpowder is burned, unburned, or partially burned and contains metal particulates, such as lead, copper, brass, and nickel.This type of GSR is used by firearms examiners to determine the distance between a gun and a target.When forensic trace evidence examiners receive a request to look for GSR on the hands or clothing of a suspected shooter, they search for primer.
The firing pin of a gun causes the shock-sensitive primer to ignite gunpowder, forcing the bullet down the barrel of the gun and on its path.The metals are removed from the primer by the heat and pressure of the cartridge.The breech area and muzzle are gas tight and Vapors escape from them.The formation of tiny metal particles is a result of the heat and cooling of this explosion.For comparison, a human hair is approximately 100 microns in diameter.A high-powered microscope is needed for finding and viewing primer GSR particles.
The gunshot particles can be easily removed.Regular activities, such as putting hands in pockets, rubbing hands together, or handling items, can wipe them away.The activity of the subject can affect the rates of loss.Depending on conditions and activity, particles may be removed from a shooter's hands within 4 to 5 hours after a shooting event.People standing within 3 feet to the side of a shooter are more likely to have GSR on their hands than people standing 10 or more feet in the same direction.The primer can travel downrange with each firing of a weapon.
In supply catalogs, investigators refer to primer GSR with lifters as dabs or stubs.Several companies sell them as a kit with gloves, instructions, an information form, and tape to seal the kit when finished.The carbon in the glue makes it able to conduct electrons.Analysts can use clear lifters, but they need an extra step of carbon coating to prevent the electron beam from hitting the sample.
There is a cap on a plastic container.The sample collection official can press the tape without ever touching it if the cap is removed.The officer who submits the information form provides the collection-site data, which includes the condition of the subject's hands, known activity prior to collection, estimated time of shooting, and the type of gun and ammunition used in the event.
One lifter should be used per collection site.Some kits have one left hand and one right hand, while others have four left back, left palm, and right palm.One lifter can suffice when sampling an entire hand, front and back.Finding particles on the left hand versus the right hand or back versus palm is meaningless because analysts don't know the activity of the hands between the shooting and the time of collection.If investigators suspect that the hands have been cleaned between shooting and collection, they can press lifters to the face, hair, or clothing.
The same type of lifters are used for sampling clothing.If the person wearing the clothes was carrying a gun in a specific location or trying to hide it, the areas of the garment for sampling would be different.Analysts avoid areas of clothing that are excessively dirty or bloody due to the fact that they can't find GSR particles.According to laboratory tests, GSR on clothing will last considerably longer than on hands, but exactly how long remains unknown and depends on the activity of the clothing and the type of fabric.
Different case-acceptance criteria can be found in forensic testing laboratories.Some may not test victims, kits unsuitable forSEM analysis, or samples collected past a time limit.The needs of the community, the importance of testing, and the cost of analysis must be assessed by each facility.The personnel, instrumentation, and time available for the work must be considered by laboratories.The FBI Laboratory no longer accepts GSR cases because it decided that its resources would be better spent fighting terrorism.
All forensic exams, including those involving fingerprints, hairs, soils, and drugs, are subject to case acceptance criteria.It is common for one GSR testing laboratory to accept victim, back and palm, clothing, and face samples, as well as those collected beyond 5 hours, while another facility does not.One laboratory may reject samples for less serious crimes while another may accept them.A drug laboratory may only test enough samples to reach the maximum charge in its jurisdiction.A firearms testing facility can't perform function tests on firearms, analyze clothing for distance determinations, or compare unfired bullets.Knowing the laboratory's case acceptance policy can help investigators maximize the use of GSR analysis results.
Police officers are trained to collect samples as soon as possible after arresting a suspect, and to clean their hands and wear gloves when sampling suspects to make sure they are not contaminated.Studies have shown that law enforcement personnel clean their hands more often than they touch their weapons, so they could be a potential source of GSR.If armed officers collect the samples, they should wear a disposable lab coat, wash their hands and wear gloves.As police vehicles and interrogation rooms are potential sources of contamination, investigators should collect GSR samples before transporting subjects in a police car or questioning them at the station.Studies have indicated a low potential for secondary transfer in these areas and that testing them occasionally may help prove the low risk.
There are safeguards that can be put in place to ensure that GSR samples are not contaminated.The firearms area of the facility should not be used for GSR testing.Before and after placement in the vacuum chamber, sample stubs are exposed to the air.The instrument functions properly if there is a positive control and a blank in the analysis.personnel place a blank lifter in the laboratory where clothing is tested for GSR to monitor the examination areaThe firearms section of the laboratory should be far away from the examination area and theSEM instrument area.No armed personnel or people who made contact with the firearms section on the day of analysis should have access to those areas.
The analysis of the stub is done with an instrument.There are at least 140 SEMs used for GSR analysis in crime laboratories around the world.Upon completion of the automated analysis, a computer stores the coordinates of each particle for manual confirmation by trained laboratory personnel.The setup and confirmation of results can take up to 6 hours, depending on the instrument and chosen parameters.The duration of analysis could increase if the sample contains a lot of particles.Once the instrument finds suspected GSR particles, the analyst relocates and manually confirms a sufficient number of them.There were documents and reports that confirmed GSR particles.
A particle has to meet certain criteria.The most important criterion is the composition of the particle.A combination of lead styphnate (Pb), barium nitrate (Ba), and antimony sulfide (Sb) in a single particle is very significant.The list of compositions allowed in primer GSR determinations is contained in the Standard Guide for Gunshot Residue Analysis.The spheroid shape of the particles is indicative of having been molten.
The source of the particle is determined by how it relates to the population of particles in the sample.Studies have shown that some exploded air bags, used brake pads, and detonated fireworks can have particles with GSR-like composition.It is possible to eliminate false positives with a comprehensive analysis of the sample.Increased confidence in GSR has been brought about by recent research and studies in the area.
A report of the findings will be issued by a forensic laboratory.Each jurisdiction abides by the rules and practices of its court system so there is no universal reporting format.The substance of a forensic report can be found in a section pertaining to findings, results, or conclusions.The results must be written in a way that is understandable to the lay person.
The submitting agency, attorneys, judge, and jury all want to know if the suspect fired a gun.The presence or absence of GSR on a person's hands cannot answer that question.All positive gunshot residue reports include a qualification, such as "The presence of primer residue on a person's hand is consistent with that person having discharged a firearm, having been in the vicinity of a weapon when it was discharged, or having handled an item with a gun."
Three or two-component particles may be referred to in a laboratory report.Any combination of those three components is included in the particles produced by most primers.When examiners find relevant particles, they should not include the word unique in the report.Even though analysts may eliminate all other sources, three-component particles containing Pb, Ba, and Sb have been proven not to be unique to gunshot residue.The examiners look for the components of the more rare ammunition types during a routine analysis.Sometimes a laboratory report will list other elements found, and analysts will compare the fired-cartridge casing in that particular case.
GSR must be reported when forensic laboratory personnel find it.While experts expect to find many particles on the hands of a shooter immediately after a weapon is fired, discovering just one particle with the correct composition should be reported.Most forensic laboratories don't use a scientifically established threshold.If the number of GSR particles does not meet established levels, examiners should report them.The threshold must be specified.It may be helpful in isolated cases to have a threshold of significance.All of the U.S. Army's cases involve personnel who carry guns.
It is difficult to interpret the results of GSR testimony.The role of teacher is assumed by an expert when describing gunshots.The examiner must present the results in a simple, honest and unbiased manner after instructing the court on the definition, production, collection, preservation, and analysis of GSR.Analysts can say that the particles came from a fired weapon, but they can't say how they were deposited on the item.The person who discharged a firearm in the commission of a criminal act cannot be identified by examiners called to testify.In cases where a suspect denies proximity to a discharged firearm, a positive GSR finding is the most reliable.A negative finding does not mean that the subject was not in the vicinity of a recently discharged firearm, only that no evidence of primer was found on the items tested.
Under the guise that negative results would be vital to the defense's strategy and ultimately exonerate the suspect, defense attorneys often raise questions as to why GSR was not collected.This argument should not be used as a driving force in requesting GSR exams that might raise more questions than can be answered effectively.
The technology behind the analysis of gunshots is scientifically sound.Since the 1970s,SEM/EDS analysis has been used in GSR analysis.Studies show that average people don't have gunshot residue on their hands, but someone who fires a gun most likely will for a period of time.The position of naming spheroid Pb, Ba, and Sb particles as having come from a fired weapon has been strengthened thanks to research.The likelihood of transfer from another source is small in most cases.The reason for analyzing is that most trace evidence is not conclusive but supportive and circumstantial.Sometimes shoeprint analyses can't identify a common source between known and unknown samples.It is worth noting that authorities located evidence with a possible common source.GSR found on the hands of a suspected shooter is significant and worthy of consideration by the jury.For a court to understand the significance of the findings, experts must discuss all aspects of sample collection, analysis, and interpretation at trial.There should be an explanation as to whether the analyst could account for any anomalies in the findings.In some cases, the sample collection officer should give testimony first to give context for the results that an analyst may report.