Nearly every criminal case the FBI and US Justice Department has reviewed during a major investigation that began in 2012 regarding an FBI lab unit has involved flawed forensic testimony, The Washington Post reported.

The review - originally spurred by a Post report in 2012 over flawed forensic testimony by Federal Bureau of Investigation lab technicians that may have led to convictions of hundreds of innocent people - was cut short last August when its findings “troubled the bureau,”according to the Post. The review was ordered by the Justice Department (DOJ) to resume this month, government officials said.

Most of the defendants in cases that involved possibly-botched testimony over microscopic hair matches were never told that their case was part of the review, which includes 2,600 convictions and 45 death-row cases from the 1980s and 1990s. In these cases, the FBI’s hair and fiber unit claimed it found a match to crime-scene samples prior to the age of DNA testing of hair.

The FBI reviewed around 160 cases before halting the investigation 11 months ago, officials said. The probe resumed once the DOJ inspector general lambasted the FBI for the delay in this investigation and another involving the same forensic unit.

A DOJ spokesman said that by last August, reviews were completed and notifications offered for defendants in 23 cases, including 14 death-row cases, that FBI examiners “exceeded the limits of science” when linking hair to crime-scene evidence.

Yet the FBI restarted the review given concerns that forensic errors applied to the “vast majority” of cases. This restart caused major delays in the investigation, leading to objections by the DOJ in January. The FBI and DOJ standoff was finally resolved this month.

“I don’t know whether history is repeating itself, but clearly the [latest] report doesn’t give anyone a sense of confidence that the work of the examiners whose conduct was first publicly questioned in 1997 was reviewed as diligently and promptly as it needed to be,” said Michael R. Bromwich, DOJ inspector general from 1994 to 1999.

“Now we are left 18 years [later] with a very unhappy, unsatisfying and disquieting situation, which is far harder to remedy than if the problems had been addressed promptly,” he added.

The reviews resumed this month under original terms based on an order by Deputy Attorney General James M. Cole, officials said.

The delay came, in part, “from a vigorous debate that occurred within the FBI and DOJ about the appropriate scientific standards we should apply when reviewing FBI lab examiner testimony — many years after the fact,” the FBI said. “Working closely with DOJ, we have resolved those issues and are moving forward with the transcript review for the remaining cases.”

Emily Pierce, a Justice Department spokeswoman, said: “The Department of Justice never signed off on the FBI’s decision to change the way they reviewed the hair analysis. We are pleased that the review has resumed and that notification letters will be going out in the next few weeks.”

Since 2012, the review has addressed only about 10 percent of the 2,600 convictions under suspicion, and maybe two-thirds of questioned death-row sentences.

The DOJ will notify defendants about misconduct in two more death-row cases and in 134 non-capital cases over the next month. The department will also complete evaluations of 98 other cases by early October, including 14 more death-row cases.

In question is a 10-member FBI unit that testified in cases across the nation that involved murder, rape, and various other violent felonies.

Though the FBI has said since the 1970s that hair evidence cannot be used as positive identification, agents still often testified to the near-certainty of matches, according to the Post. Ultimately, there is no accepted research regarding how often hair from different people can appear as the same. Today, the FBI uses visual hair comparison protocols to rule out a potential suspect as a source of hair found at a crime scene before using more accurate DNA testing.

The review highlights a hesitance among courts and law enforcement to address systemic faults of forensic testimony and methods from bygone eras.

“I see this as a tip-of-the-iceberg problem,” said Erin Murphy, an expert on modern scientific evidence who teaches at New York University.

“It’s not as though this is one bad apple or even that this is one bad-apple discipline,” she said. “There is a long list of disciplines that have exhibited problems, where if you opened up cases you’d see the same kinds of overstated claims and unfounded statements.”