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 bureau experts to more precisely describe the significance of their findings in court.
The 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's publication next month could open the door to hundreds, even thousands of appeals, and give defense lawyers in future cases new ammunition for undermining expert testimony.
The National Association of Criminal Defense Lawyers said Friday it will urge its members to aggressively seek appeals in past cases where bullet lead analysis was done. "There are people sitting in jails who were wrongly convicted because of this junk science," spokesman Daniel Dodson said.
Barry Scheck, the group's president-elect who as a lawyer has worked to free prisoners convicted by errant science, praised the FBI for seeking the review. "The FBI should go through their own case files and reopen every case where this kind of analysis was done," he said.
Senate Finance Committee chairman Charles Grassley, R-Iowa, urged the academy to quickly release its findings. "Flawed forensic techniques risk letting the guilty go free and sending the innocent to prison. This report needs to be made public so Congress and others can evaluate what's happened and hold the FBI accountable," Grassley said.
FBI officials said they had not seen the report and would not comment.
"I cannot comment on a draft report that is still being peer reviewed and subject to change," added National Academy of Sciences spokesman Bill Kearney.
Officials familiar with the report said it is finished, save for an issue involving statistical analysis.
The findings are the latest in a string of controversies and embarrassments this year to hit the FBI lab, which pledged to remake itself after a scandal in the 1990s over bad science.
One FBI lab scientist involved in lead bullet analysis has pleaded guilty to giving false testimony, another employee has admitted to improper DNA testing and long-secret documents have emerged this year suggesting there were undisclosed problems with the FBI lab's work in the Oklahoma City bombing case.
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 academy, chartered by Congress and privately run, is widely respected.
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, especially given that the bureau does not have information on how many bullets from the same lead source may have been distributed in an area around a crime scene.
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 had warnings prior to the academy study. Retired FBI metallurgist William Tobin published research challenging the very premise of the FBI's science. And Iowa State University 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.