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Firearms and Toolmarks
Transcript of Firearms and Toolmarks
Eva Salmeron Firearms and Tool marks FLASHBACK
Where were you? Beltway Snipers The Beltway Snipers * October 2, 2002- October 22, 2002
~ The DC Metropolitan Area was hit by a series of shootings that left 10 dead and 3 injured.
~ The public feared for their own lives.
~The police had no leads and believed the "sniper" traveled in an old white van.
~ The police also believed there was one sniper.
There were TWO! The Attacks John Allen Muhammad and Lee Boyd Malvo went on a rampage, killing ten. After capture, Malvo states that the attacks were a plan to capture children and teach them how to terrorize America. The capture Firearms Due to the frequent use of firearms in crime scenes, the evidence left behind can be very beneficial to investigators. Firearms can leave behind valuable evidence such as bullets, cartridge cases, and gunpowder residue. Also, serial numbers can also be valuable when solving a crime. Firearms identification must extend beyond the comparison of bullets, cartridges, and the gun from which the bullet was shot. Bullet and Cartridge Comparisons Automated Firearms Search Systems Area attacked. Tool marks A tool mark is any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object. By examining bullet striations, investigators can link a bullet to a weapon, and ultimately link a suspect to a crime. The gun barrel is a solid steel rod hollowed out by a drill. The drilling gives the barrel random microscopic markings, individualizing each barrel.
Rifling is used to impress the inner surface with spiral grooves. The grooves help guide the bullet through the barrel, keeping it from tumbling over the end. This makes the barrel and discharged bullet even more unique and makes the bullet easier to link to a gun.
Also the caliber of a gun - the distance from opposite lands in a gun barrel, can be used to link a bullet to a gun. The caliber is measured in hundredths of an inch or in millimeters. Comparing Bullet Markings Because there is not practical way of comparing the markings on the bullet to the striations on the bore (inner gun barrel), test shots are fired to compare the test bullet markings to the evidence bullet markings.
To prevent damage to the test bullet markings and to facilitate bullet's recovery, test firings are normally made into a recovery box filled with cotton or into a water tank.
Any differences in lands, grooves, and their direction of twist (class characteristics) immediately eliminate the possibility that both bullets traveled through the same barrel.
If the class characteristics are the same, then a comparison microscope is used to match striated markings on both bullets. Considerations in
Bullet Comparison The presence of grit and rust can distort markings on bullets shot through the same barrel. Recovered bullets become so mutilated upon impact that they yield only a small area with intact markings. Striation markings on barrels are subject to change due to wearing. However, changes are not dramatic and don't affect the matching of bullets. The final opinion is based on the knowledge, judgement, and experience of expert. Cartridge Cases Bullet shells are also impressed with striation markings.
The firing pin, breechblock (rear end of gun barrel), the extractor (mechanism by which case is withdrawn from chamber), and the ejector (mechanism that throws cartridge or fired case from the firearm) impress markings on the spent cartridge case.
Cartridge cases are just as valuable in link guns to a crime. Gunpowder Residue
and Vapor Similar to fingerprint files.
Early 1990s, both FBI and Bureau of of Alcohol, Tobacco, Firearms, and Explosives (ATF) had two incompatible and competing computerized databases, DRUGFIRE, and the Integrated Ballistic Identification System (IBIS), respectively.
In 1999, both systems were combined to make National Integrated Ballistics Information Network (NIBIN). ATF has overall responsibility for system sites. Tool marks are mainly found at crime scenes that are burglaries where forced entry is involved. Comparing Tool Marks The size and shape of a tool can be determined from the examination of the impression left behind.
But the size and shape of a tool is not enough to allow examiners to identify a single tool used at a crime scene.
What individualizes each tool are the imperfect characteristics it has caused by wear & usage, manufacture errors, or damage; and can be seen microscopically.
The shape and pattern of such imperfections are further modified by damage and wear during the life of the tool; and most importantly are expressed in the tools impression. Most commonly crowbars or screwdrivers are used to pry open window frames or doors.
Other types of tools: bolt cutters, chisels, scissors, pliers, wrenches, saw, knives, and etc. Persevering the evidence The comparison microscope is used to compare crime-scene tool marks with test impressions made with the suspect tool.
For examination, the entire object with the impression should be submitted to the crime laboratory.
Liquid silicone casting material is then used to fill and impression to reproduce fine details of the mark.
Investigators should never touch or fit suspected tool into impression, it may alter mark and damage evidence. Other Impressions Shoe, tire, or fabric impressions are also found at crime scenes.
Shoe and tire marks impressed into soft earth at a crime scene are best preserved by photography and casting.
Chemical enhancement can visualize latent or nearly invisible blood impressions. Bibliography Richard Saferstein, R. S. (2007). Firearms, tool marks, and other impressions. In Forensic Science An Introduction (1st ed., Vol. 1st, pp. 506-545). Upper Saddle River, New Jersey: Prentice Hall PTR.
http://en.wikipedia.org/wiki/Beltway_sniper_attacks When tools are used at a crime scene they can be linked to the unique tool marks. A bullet is propelled through the gun barrel due to expanding gases cause by the ignition of smokeless powder or nitrocellulose. All of the powder, however, does not get turned into gas and therefore is projected with the bullet.
Gunpowder residue can be very useful in distance determination (distance from firearm to target).
Analysis of gunpowder residue can differentiate between a homicide and a suicide in cases involving gunshot wounds. Can also help determine suspect and victim's credibility.
Blowback of gases can also be useful in distance determination too. Serial Number Restoration Forensic scientists can use chemical and physical processes to restore or enhance damaged characters of a serial number on a gun.
Forensic scientists will first polish the metal part of the gun with a sand-paper type material to remove chips of metal from the surface.
Next they will apply chemical reagents to etch the metal until the number is restored. The scientist will select the proper chemical based on the variety of metal surface. For example, different chemicals are used to etch different alloys such as aluminum, zinc and steel. Collection and Preservation Primer Residue on the hands Firearms should be packaged in an envelope or paper bag separate from the ammunition. The ammunition and magazine should be placed in a paper envelope or bag.
Casings and bullets should be packaged separately and placed in paper envelopes or small cardboard pillboxes. When a shot is fired, gunpowder and vapor are propelled backwards toward the shooter. Finding gunshot residue on a suspect's hand can help determine whether a suspect fired the shot or if another person was within close range.
Investigators apply adhesive tape to collect the residue and a SEM (Scanning Electron Microscope) to analyze it. However, excessive operator times have deterred the use of a SEM.
Also, cotton swabs moistened with a 5% nitrate solution may also be used. Since this test may be susceptible to contaminants such as urine, fertilizers, and cosmetics, many forensic labs don't use this technique. * The police went on no leads.
*Muhammad and Malvo went unnoticed for about 3 weeks.
* On October 24th, 2002 near interstate 70, both were found sleeping in an blue 90' chevy caprice.
* Upon closer examination of the vehicle, police found A Bushmaster .223-caliber weapon and bipod in the trunk.
* With bullet striation examination, the guns were used in 11 of the 14 shootings. Both were arrested and charged. The Prosecution * Malvo and Muhammad began their trials in 2003.
*Since Malvo was only 17 when he committed the crimes he could not face capitol punishment.
*The court pushed for Muhammad to be extradited to Virginia.
*Muhammad was sentenced to death by legal injection on September 16th, for November 10,2009.
*On November 10, 2009 at 9:11pm, John Allen Muhammad was pronounced dead.
* Malvo was convicted for six consecutive life sentences without the possibility of parole.