The Debate
Not enough research has been done to know the probability of error in ballistics matching. So it's impossible to say with certainty that the marks made on bullets as they are fired are truly unique to an individual gun. Currently, ballistics examiners are aided by computer databases such as the ATF's National Integrated Ballistic Information Network, but lab techs always rely on their own visual inspection to make the final call. The Association of Firearm and Tool Mark Examiners only requires an examiner to find "sufficient agreement" between bullets in order to conclude that they came from the same gun. Those judgment calls can cause false results. Last September the Detroit Police Department's crime lab was shut down after an audit by the state of Michigan found a 10 percent error rate in ballistics identification.