FBI Defends Bullet Matching

The FBI mounted a vigorous defense Monday of a forensic method it has used for more than 30 years to link bullets found at crime scenes to those owned by criminal suspects.

The comments came at the first meeting of an expert panel of the National Research Council, a branch of the National Academies of Science. The 11-member committee will review the FBI’s procedures for comparing bullets based on minute impurities found in lead.

Bullet matching has helped convict hundreds of defendants, but has been criticized recently by independent experts and former FBI laboratory examiners, who say the bureau’s use of the technique is scientifically unsupported.

The FBI tests the lead in bullets found at crime scenes for traces of contaminants or additives, such as tin and antimony. It compares the results to those for bullets found in a suspect’s possession. In trying to match bullets, laboratory personnel look for whether the same trace elements are present in the same concentrations. FBI examiners have often stated or implied in court that they can trace a bullet to a specific manufacturing batch -- even to a particular box.

The technique has offered authorities a way to solve crimes involving gun violence even when no gun could be found. It has often strengthened prosecutors’ weakest cases -- those where evidence is scarce or circumstantial.

Recent research, however, has cast doubt on the significance of matches. Researchers have found that bullets made from the same block of lead can vary in their trace elements, while those produced years apart can appear virtually identical.

At Monday’s hearing, Robert D. Koons, an FBI research chemist, said the bureau stands by the many years of courtroom testimony by its laboratory examiners.

The FBI expects the study “to provide a reference for legal acceptance” of bullet matching, Koons said.

However, he disavowed the notion that lead analysis can trace a bullet to a particular box of ammunition. “You never can definitively say, ‘This bullet came from this box,’ ” Koons said.

He said that bullet lead evidence, though not as definitive as positive identification, such as a clear fingerprint, is nevertheless useful.

Richard K. Gilbert, a criminal defense attorney in Washington who has challenged bullet-lead evidence in court, criticized the bureau for refusing to release its protocol, or scientific procedures, for lead analysis, which he said makes independent evaluation impossible.

An FBI official said the bureau might allow the panel to review the protocol confidentially.

The National Research Council created the panel at the FBI’s request. It is expected to issue a report in July.

“Our question is, ‘What is the significance of this evidence,’ ” said panel member Paul C. Giannelli, a law professor at Case Western Reserve University in Cleveland. Although the FBI is paying for the committee’s work, “our client is the public,” he said.