A new report by the National Research Council finds that the methodology used by the FBI to match bullets is flawed. For background on the issue, see our report here.

A panel of government scientific advisers has found that an FBI forensic technique long used to link bullets with assailants is scientifically flawed and potentially misleading to juries, a finding that could affect hundreds of convictions.

The method, which measures the likelihood of a chemical match between bullets found at crime scenes and those in the possession of a defendant, has been used for more than three decades. The Los Angeles Times obtained a draft summary of the report, which is expected to be released by the National Research Council (NRC) in December.

....FBI examiners have often stated or implied in court that a bullet can be traced to a specific manufacturing batch — even to a particular box.....The NRC panel substantially agreed with recent research indicating that bullets from the same source of lead can significantly vary in their chemical makeup, and bullets from different sources — even those manufactured years apart — can share nearly identical amounts of trace elements.

The finding contradicted some prosecutors' depictions of each batch of lead as being unique, like a snowflake or fingerprint. The study suggests the number of "matching" bullets was impossible to determine and could be in the tens of millions or higher — reducing the significance of a match.