A man was shot. Police found a gun inside the yard of a nearby home. A lab tested the gun and compared the grooves and scratches of its interior to the casings found at the crime scene. According to the examiner, the gun conclusively matched "to the exclusion of every other firearm in the world." End of story. Guilty verdict.
But how is this possible? Is it without a doubt that the casings didn't come from another gun?
It's not, but sadly forensic examiners for years have been able to say that "close but not identical ballistic markings" are in fact conclusive. Countless juries have been told that something is a match without also being told the percentage of uncertainty.
The New York Times recently profiled a story about this common practice-one that has contributed to wrongful convictions all across the country.
The Times article pointed out a 2009 finding by the National Academy of Sciences, a nonprofit organization that conducts research in science and technology. In a nutshell, the NSA basically concluded that there is no single forensic method utilized today that can link evidence to an individual with a high degree of certainty. Whether it's linking footprints to a person's shoe or a shell casing to a gun.
Since then, pattern evidence has been closely scrutinized.
In May 2015, a $30 million grant by NIST was given to a team of statisticians and legal professionals tasked with analyzing matches to determine the likelihood of, for instance, a hair sample to that of another individual or bite mark to that of another person's teeth.
Almost a year later, the team is still at work. Researchers are putting together an enormous database to house the countless images need to conduct the analysis.
They hope that examiners will be able to eventually come up with a similarity ratio to provide to juries. However, it remains to be seen how it will work and for what patterns. But when lives are on the line, it's worth pursuing.