Category Archives: Firearms

Forensic Firearms Identification

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Silver to bullets

Poster printed by Sir Joseph Causton & Sons, Ltd, London, 1915. Source: Library of Congress.

Forensic firearm examiners determine whether a certain weapon fired a bullet or cartridge found at a crime scene. Early efforts linked spent ammunition with a class of weapon. Following the 1862 shooting of Confederate General Stonewall Jackson, for example, investigators concluded that the General had been accidentally shot by his own side. The spherical projectile removed from the General had been fired from a smooth-bore musket, a type of weapon that the Union Army no longer used.

In 1912, Professor Victor Balthazard at the University of Paris formulated the basic principles of firearms examination. Using enlarged photographs, he compared marks created by a firearm on the surface of bullets and cartridge cases found at a crime scene with marks on ammunition that he had fired from a suspect weapon. In this way, he could connect crime scene ammunition to a particular firearm.

During the 1920s in New York, four men rediscovered Balthazard’s principles and initiated modern firearms identification: Charles E. Waite, Calvin Goddard, Philip O. Gravelle, and John E. Fisher. Gravelle had extensive experience with a comparison microscope to study fine details in cloth patterns. He suggested that they might be able to use the instrument to compare fired bullets and cases.

In a signal event of firearms identification, the group bought two comparison microscopes and modified them. They added a comparison bridge, and rotatable mounts for bullets and cartridge cases. Through the eyepiece of the bridge, two pieces of spent ammunition could be examined, one on each stage of the two microscopes.

Police departments and the courts became aware of the value of “fingerprinting” bullets, especially after Goddard testified about his findings in the 1929 St. Valentine’s Day Massacre. Within a decade, firearms identification became an established technique of criminal investigation.

Microstamping Could Yield Macro Benefits

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Example of microstamp placement

 

Traditional firearm identification is based upon the fact that every weapon has unique features introduced during manufacture and later caused by wear. These characteristics of a firearm create striated and impressed marks on fired ammunition that enable an examiner to identify a round of fired ammunition as coming from a particular gun. This analysis requires an examiner to have access to a suspect firearm that can be test fired to produce a bullet and cartridge case.

A method called microstamping could radically change firearm identification practice. Using lasers, unique alpha-numeric codes are added to certain parts of a firearm, such as the firing pin and breech face, and these identifiers are stamped onto a cartridge when fired. A code could reveal a firearm’s manufacturer, model, and serial number. The serial number alone would lead investigators to the identity of the person who first purchased the firearm.

Proponents of microstamping claim that the technique would not only aid a criminal investigation, but also would reduce the supply of illegal firearms. Microstamping, the argument goes, would deter people with clean records (straw buyers) from purchasing guns for criminals.

Since the technique was proposed, microstamping has generated controversy about the method’s reliability. A study posted on the New Yorkers Against Gun Violence website indicates that microstamping works.

GSR Speaks Again

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Traditionally, gunshot residue contained gunpowder residues (such as partially-burned or unburned gunpowder) and lead residues. However, an increasing number of ammunition manufacturers produce ammunition that contains little or no lead. This change is good for the environment, but creates a challenge for criminal investigators, because crime labs test for gunshot residue by detecting the presence of lead, barium, and antimony.

During June 2012, forensic researchers at Florida International University announced a new technique that can potentially link a suspect to fired ammunition by identifying the chemical signature of the powder inside a bullet. In this approach, a chemist analyzes the chemical composition of a bullet’s smokeless powder. The method reveals the particular formula of the smokeless powder, which further identifies the manufacturer of the powder.

“Crime labs all over the country are faced with the reality that their only way to analyze whether a gun was fired by a suspect may become obsolete,” said chemistry Professor Bruce McCord in a press release. “Our discovery is not only more accurate, but it can determine the type of gunpowder used in a crime even if the gun is never recovered.”

GSR Speaks

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Gas precedes a fired bullet.

When a bullet leaves the muzzle, it is preceded by a gas bubble. Source: Alexander Jason, “Effect of Hair on the Deposition of Gunshot Residue,” Forensic Science Communications 6(2) (April 2004).

In a shooting, gunshot residue (GSR) can be found on the victim, on surfaces within a few feet of the sides of the firearm, and on the hands of the shooter. The excellent FirearmsId.com website offers a brief description of GSR generation:

When the firing pin of a firearm strikes the primer of a cartridge the primer compound ignites sending a flame into the cartridge case. Gunpowder in the cartridge case starts to burn, causing it to change from a solid material to a gas. This change creates pressure within the cartridge, which in turn forces the bullet down the barrel and down range. Pressure building behind the bullet is released when the bullet exits the muzzle of the firearm.

The bullet acts like the cork in a shook up Champagne bottle. When the bullet exits the muzzle, pressure behind it blows the gunshot residues out of the firearm’s barrel under high velocity. The residues are expelled from the barrel in a smoky cone shaped pattern.

Analysis of GSR can establish that a shooting took place and may link a person with that shooting. One day, GSR may reveal more details about a shooting. On June 18, 2012, University at Albany (New York) researchers announced that they developed a method to determine the caliber and type of weapon used in a crime by analyzing GSR. The technique uses spectroscopy with laser light. Lead researcher Igor Lednev cautioned that his team must continue their research before the method can be presented in a courtroom.