The Justice Department will expand its review of forensic testimony by the FBI Laboratory in closed criminal cases nationwide to ensure it has not overstated evidence against defendants, Deputy Attorney General Sally Yates announced.

In March, the department will lay out a framework for auditing samples of testimony that came from FBI units handling pattern-based evidence, such as tracing the impressions that guns leave on bullets, shoe treads, fibers, soil and other crime-scene evidence, department officials said this week. The FBI and other crime labs nationwide conduct more than 100,000 such examinations each year.

Justice Department officials left open questions of which techniques and how many cases would be reviewed, using what standard over what time period, and whether convicted defendants would be notified if any errors are found.

Yates linked the move to an FBI and department finding last year that nearly all FBI hair examiners overstated testimony about hair matches incriminating defendants during the two decades before 2000.

[FBI admits flaws in hair analysis over decades]

“We are undertaking this quality-assurance review because we think it is good operating procedure — and not because of specific concerns with other disciplines,” Yates said Wednesday in an address to the American Academy of Forensic Scientists’ annual meeting in Las Vegas.

Hundreds of convicted defendants in hair-match cases have been notified of the testimony errors, and the bureau and the department are offering them new DNA testing and lowering barriers to appeals.

Determining “whether the same kind of ‘testimonial overstatement’ . . . could have crept into other disciplines” would help “ensure the public’s ongoing confidence in the work we do,” Yates said.

[Convicted defendants left uninformed of forensic flaws found by Justice Dept.]

A spokesman for the FBI Laboratory declined to comment.

In a statement, Sen. Patrick J. Leahy (Vt.), ranking Democrat on the Senate Judiciary Committee, applauded the Justice Department “for taking responsibility and launching a full review so that the public can learn exactly what went wrong and how we can prevent this from ever happening again.”

Yates’s proposal is among the broadest responses yet to a National Academy of Sciences panel report in February 2009 that questioned subjective comparisons of evidence by experts. The panel concluded that although examiners had long claimed to be able to match pattern evidence to a source with “absolute” or “scientific certainty,” only DNA analysis had been validated through statistical research.

[Forensic techniques not as reliable as you may think]

The Obama White House in 2013 appointed a National Commission on Forensic Science to respond to the National Academy of Sciences’ call to strengthen standards for research, labs and examiners. Yates said the department plans to submit a suggested framework for the testimony review at the commission’s March 21 meeting. The commission would help define the scope of the audit and respond to any errors found, Yates said.

[U.S. to commit scientists and new commission to fix forensic science]

Despite criticism from academics, courts have continued to allow the other types of forensic evidence.

Yates acknowledged disagreement among practitioners over how to make complex scientific concepts more understandable for judges and juries, without either exaggerating or understating the value of findings.

“We recognize this is no simple task, and we want to make sure we do this review in a deliberate, thoughtful and transparent way,” Yates said.

Victor W. Weedn, outgoing AAFS president and chairman of the George Washington University department of forensic sciences, said, “To critique old cases, to see the limitations of old techniques we used because of advances in technology is a matter of transparency and accountability, and to not sweep it under the rug, that is a breath of fresh air.”

The department and FBI’s partners in the hair review praised Yates’s decision.

The National Association of Criminal Defense Lawyers was “pleased” that the department had committed to “involve outside experts and the scientific community” in the development of standards, senior resource counsel Vanessa Antoun said in a statement.

Peter Neufeld, co-director of the Innocence Project, a nonprofit legal clinic, also commended Yates’s decision, saying an essential element “will be to recruit independent and external experts in the fields of statistics and probability.”