Scientific panel- FBI bullet analysis flawed

WASHINGTON -- The National Academy of Sciences has concluded that a technique the FBI has used for decades to match bullets to crimes is flawed, a position that could hand defense lawyers a new avenue of attack against the world's most famous crime lab.

The academy's study, to be released early next month, makes about a half-dozen recommendations for changing the way the FBI matches bullets by their lead content and strongly urges the bureau's experts to more precisely describe the significance of their findings in court.

FBI lab director Dwight Adams asked for the academy study this year after one of the bureau's former metallurgists began questioning the validity of the science used by the lab to match bullets by their lead content.

The science is based on the theory that bullets from the same lead batch share a common chemical fingerprint. Adams told AP last spring he was confident the study would vindicate the bureau's science.

But the study, according to those who have seen it, strongly challenges some of the assumptions and techniques that the FBI has used since around the time of John F. Kennedy's assassination.

For instance, it urges the bureau to stop a practice known as data chaining that its chemists have used in the past to improve the likelihood they could match two bullets through chemical analysis.

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 match identically. Said another way, the FBI can match two slightly dissimilar bullets if they can find a third -- from a manufacturer, for instance -- that matches both.

Charles Peters, an FBI expert witness in cases involving bullet lead comparison, testified recently that data chaining -- the technique disavowed by the academy -- was important.

"I'm a fan of chaining," 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."

Citing examples of inconsistent or contradictory testimony by FBI experts in courtrooms, the study also recommends that lab analysts' work and testimony be reviewed by a colleague to ensure accuracy and precision, the sources said.

And it strongly urges FBI expert witnesses to more narrowly and precisely describe the scientific significance of lead bullet findings.

The FBI has been the prime practitioner of lead bullet comparisons in the United States, and has used them for decades. A database of lead test results kept by the agency had more than 13,000 samples in the late 1990s, FBI officials have told the AP.

The FBI most commonly identifies bullets recovered from a crime by firing new bullets from the suspect's weapon and comparing the markings left by the gun barrel on the test bullet with the crime scene bullet. But that method only works when the crime scene bullet is in good shape or if police have the suspect weapon.

In cases where recovered crime scene bullets are fragmented or disfigured or a suspect's weapon is unavailable, the FBI has turned to chemical analysis to try to determine whether the bullet's lead content is comparable to the same manufacturer, lead source or box of bullets connected to the suspect.

The FBI has had several warnings prior to the academy study about lead bullet analysis. Retired FBI metallurgist William Tobin published research stating that bullets from the same lead source had different chemical makeups and bullets from different lead sources appeared chemically similar, challenging the very premise of the FBI's science.

And Iowa State University has conducted research that drew similar conclusions.

"The fact that two bullets have similar chemical composition may not necessarily mean that both have the same origin," that study said.