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Broward County Sheriff’s Office to Use Unreliable Forensic Method

According to a recent article by the South Florida Sun-Sentinel, the Broward County Sheriff’s Office plans to test guns that were found or seized by police, but which aren’t necessarily evidence of a crime.

While many people are not aware of this, police departments across the country routinely take possession of firearms that are not used as evidence. Some guns are found discarded, others are seized during domestic violence or drug arrest, and sometimes guns are recovered during community “buy back” programs. Once recovered, a firearm is stored by the police for a period of time and then later destroyed – unless of course it is being preserved as evidence in a criminal prosecution.

By randomly testing its “non-evidentiary” guns, Broward crime scene technicians hope to discover clues that may help solve some open cases. By recovering a projectile from a gun test fired in their laboratory, crime scene technicians are able to compare the markings imprinted on the projectile by the gun’s barrel to the markings on other bullets retrieved from crime scenes. When the imprints on the bullets seem to match, technicians presume that the bullets were fired from the same gun. In a sense, crime scene technicians compare the unique markings of a gun barrel to a person’s fingerprints.

This type of forensic evidence is called “pattern evidence” and is very different from “analytical evidence” which concerns DNA analysis, blood toxicology, and the like.

While the concept of comparing barrel imprints on projectiles seems very compelling, the truth is that pattern evidence is unreliable. Unlike DNA or blood analysis, pattern evidence calls for interpretation by someone who visually inspects two samples and opines that they look similar enough to be considered matches.

This methodology becomes especially problematic because the two samples a technician may look at are rarely, if ever, identical. Unlike what is seen on TV, a bullet recovered from a crime scene looks nothing like the perfect specimen recovered in a laboratory. Bullets often fragment, chip, flatten, and partially disintegrate upon impact. This is especially problematic when dealing with hollow point ammunition (which mushrooms inside its target) or jacketed ammunition which separates on impact. Not to mention the fact that surviving portions almost always receive additional imprints, scratches, and dings from the targets they travel through and ultimately land in.

In 2005, the United States Congress ordered the National Academy of Sciences to conduct a study on forensic science to address problems like these. For those who have never heard of the National Academy of Sciences, they are kind of a big deal and have been advising the Federal government on scientific and technical matters since Congress created the Academy in 1863.

In its 350 page report to Congress, the National Academy of Sciences stated that “[W]ith the exception of nuclear DNA analysis, however, no forensic method has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between evidence and a specific individual or source.” See: Strengthening Forensic Science in the United States: A Path Forward, Page 7, The National Academy Press, 2009.

This is a huge problem!

While investigators should analyze each and every clue they recover from a crime scene, police have a tendency to overstate the value of their evidence when trying to close a case – especially when they try to build a case around a particular suspect. This problem is exacerbated when a shortcoming in evidence can be ignored by labeling the evidence “scientific” or “forensic.”

Science plays a very important role in law enforcement and in our court system. However, the public, especially those who serve on juries, should always question what they are being told. This scrutiny should be applied to both prosecutors and defense lawyers alike. Each piece of evidence in a case, whether it is evidence that supports guilt or negates guilt, should only be given its proper weight, if any at all.

Ultimately, jurors should remember that the burden of proof rests on the prosecutors and the prosecutors alone. As the accuser, it is the prosecutor’s job to prove each and every element of a crime to the exclusion of every reasonable doubt. If a juror has reasonable doubt about the true scientific validity of a piece of evidence, then that evidence should be disregarded.

When it comes to scientific evidence, I for one put my faith in the National Academy of Sciences and you should too.

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