WASHINGTON (CBS/AP) — The Justice Department and FBI on Monday pledged an independent review of FBI laboratory protocols and procedures following the discovery of flawed forensics testimony in hundreds of older criminal cases.

The investigation will look at how the scientific problem occurred and “why it was allowed to continue for so long,” the Justice Department said. Law enforcement officials also said they would review hundreds of additional cases in which scientifically invalid testimony may have been given and would encourage states whose examiners were trained by the FBI to conduct their own reviews.

The steps, outlined in a joint statement with the Innocence Project and the National Association of Criminal Defense Lawyers, follow revelations of flawed testimony by specialized FBI examiners in cases.

The FBI and the Justice Department have been reviewing criminal cases where microscopic hair analysis was used to connect a defendant to a crime following the exoneration of three men convicted at trial. The investigation covers cases prior to 2000, when more accurate DNA analysis became routine for the FBI.

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Of the 268 trials that have already been reviewed in which hair evidence was used against a defendant, more than 95 percent contained flawed testimony by specialized examiners. In addition, 26 of 28 FBI specialists provided flawed statements at trial or produced lab reports with errors, the FBI said. The majority of affected cases are state prosecutions.

“The Department (of Justice) and the FBI also are committed to ensuring the accuracy of future hair analysis testimony, as well as the application of all disciplines of forensic science,” Amy Hess, executive assistant director of the FBI’s science and technology branch, said in a statement. “The Department and FBI have devoted considerable resources to this effort and will continue to do so until all of the identified hair cases are addressed.”

The errors in testimony do not necessarily establish a defendant’s innocence, but the legal groups say they’re working with the Justice Department to alert defense lawyers of the review and to make sure that defendants in affected cases would have a way to challenge convictions.

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