Study criticizes FBI bullet-match method

ASSOCIATED PRESS

In a finding that could affect thousands of criminal cases, the National Academy of Sciences has concluded that some techniques the FBI has used for decades to match bullets to crimes are flawed or imprecise.

The study, expected to be released in the next few weeks, makes about a half-dozen recommendations to improve the FBI lab’s science used to match bullets through their lead content.

The academy’s findings, which are in final-draft form, were described to the Associated Press by several people involved in the study. They would speak only on condition of anonymity.

The study specifically urges the bureau’s chemists to stop a practice known as data chaining, which chemists have used to match bullets to a crime.

In data chaining, scientists can conclude that if the lead content of bullet A matches bullet B, and bullet B’s content matches bullet C, then it is safe to testify that bullet A and bullet C are a match, even if their test results don’t directly match. Said another way, the FBI can match two dissimilar bullets if it can find a third — from a manufacturer, for instance — that matches both.

The FBI science relies on the theory that bullets from the same batch of lead share a common chemical fingerprint.

Charles Peters, an FBI expert witness in cases involving bullet lead comparison, testified recently that data chaining was important to matching bullets.

“I’m a fan of chaining,” Mr. Peters testified in April in a case in Alaska. “If we had great precision, really good precision, … and we didn’t do something like chaining, or something like that, nothing would ever match.”

A reference in the latest draft of the academy report indicates that the FBI may abandon the data-chaining technique, the sources said. FBI officials said Thursday night that they had not seen the report and could not comment on it.

“I cannot comment on a draft report that is still being peer-reviewed and subject to change,” National Academy of Sciences spokesman Bill Kearney said Thursday.

Citing specific examples of conflicting or inconsistent testimony by FBI experts, the study also recommends that lab analysts’ work and testimony be reviewed by a peer to ensure accuracy and precision, the sources said.

The FBI lab’s director has been trying to increase the number of peer reviews inside the lab.

The academy’s recommendations are likely to have a huge impact, opening the door for appeals from defendants convicted in cases in which bullets were matched by the FBI using lead analysis. It also could force FBI-lab witnesses to more narrowly describe the statistical significance of their findings in future cases.

Story Continues →