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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.

Dealing with DNA Evidence

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DNA in a bottle

Source: U.S. Department of Energy Genomic Science program.

In his book, The Blooding (1989), Joseph Wambaugh described the first use of DNA testing in a criminal investigation. As it turned out, the new type of forensic analysis unveiled a rapist-killer in an unusual way. The police collected blood samples for DNA testing from every male between the ages of 16 and 34, living in the vicinity of the crime scenes. To dodge the test, a cake decorator named Colin Pitchfork paid a coworker to donate blood for Pitchfork. After the police learned about the ruse, they arrested Pitchfork, who confessed to the crimes.

Since then, DNA testing has become routine in both criminal and civil cases. Readers of mystery and crime fiction expect DNA analysis to play some role in a story set in modern times. One good source for basic information on DNA testing is the U.S. Department of Justice’s DNA for the Defense Bar. As the title indicates, the guide is particularly useful if your main character is a defense attorney who must confront damaging DNA evidence. The book is available at the National Institute of Justice website.

Introduction to Fingerprints

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Image from Henry's book

Image of a whorl pattern that appears in Henry’s book. (Source: National Library of Medicine).

One of the oldest types of evidence used in criminal investigations is the fingerprint. During the 1870s, Henry Faulds, a Scottish doctor working in a Tokyo hospital, studied fingerprints as identifying marks. After he applied his research in a criminal case, Faulds offered to fund a fingerprint bureau at Scotland Yard. But police officials were not interested.

Faulds published his observations about fingerprints in 1880. The report came to the attention of Francis Galton, a nephew of Charles Darwin. Galton investigated fingerprints and concluded that fingerprints remain the same during an individual’s lifetime, and that no two fingerprints are identical. He suggested a system of fingerprint identification in his book, Finger Prints (1892).

Eight years later, Edward R. Henry, Commissioner of the Metropolitan Police, published his book, The Classification and Use of Finger Prints, which also proposed a method of fingerprint classification. New Scotland Yard launched a three-person Fingerprint Branch in July 1901. The department used the Henry system of classification, which has become the core of fingerprint systems in most English-speaking countries.

Prepared by the International Association for Identification, The Fingerprint Sourcebook (2011) is an excellent resource for many aspects of fingerprint identification practice. The National Institute of Justice offers a free copy of the book on its website.