Correction: Earlier versions of this story gave the wrong middle initial for former federal prosecutor Michael R. Bromwich.

Justice Department officials have known for years that flawed forensic work might have led to the convictions of potentially innocent people, but prosecutors failed to notify defendants or their attorneys even in many cases they knew were troubled.

Officials started reviewing the cases in the 1990s after reports that sloppy work by examiners at the FBI lab was producing unreliable forensic evidence in court trials. Instead of releasing those findings, they made them available only to the prosecutors in the affected cases, according to documents and interviews with dozens of officials.

In addition, the Justice Department reviewed only a limited number of cases and focused on the work of one scientist at the FBI lab, despite warnings that problems were far more widespread and could affect potentially thousands of cases in federal, state and local courts.

As a result, hundreds of defendants nationwide remain in prison or on parole for crimes that might merit exoneration, a retrial or a retesting of evidence using DNA because FBI hair and fiber experts may have misidentified them as suspects.

In one Texas case, Benjamin Herbert Boyle was executed in 1997, more than a year after the Justice Department began its review. Boyle would not have been eligible for the death penalty without the FBI’s flawed work, according to a prosecutor’s memo.

The case of a Maryland man serving a life sentence for a 1981 double killing is another in which federal and local law enforcement officials knew of forensic problems but never told the defendant. Attorneys for the man, John Norman Huffington, say they learned of potentially exculpatory Justice Department findings from The Washington Post. They are seeking a new trial.

Justice Department officials said that they met their legal and constitutional obligations when they learned of specific errors, that they alerted prosecutors and were not required to inform defendants directly.

The review was performed by a task force created during an inspector general’s investigation of misconduct at the FBI crime lab in the 1990s. The inquiry took nine years, ending in 2004, records show, but the findings were never made public.

In the discipline of hair and fiber analysis, only the work of FBI Special Agent Michael P. Malone was questioned. Even though Justice Department and FBI officials knew that the discipline had weaknesses and that the lab lacked protocols — and learned that examiners’ “matches” were often wrong — they kept their reviews limited to Malone.

But two cases in D.C. Superior Court show the inadequacy of the government’s response.

Santae A. Tribble, now 51, was convicted of killing a taxi driver in 1978, and Kirk L. Odom, now 49, was convicted of a sexual assault in 1981.

Key evidence at each of their trials came from separate FBI experts — not Malone — who swore that their scientific analysis proved with near certainty that Tribble’s and Odom’s hair was at the respective crime scenes.

But DNA testing this year on the hair and on other old evidence virtually eliminates Tribble as a suspect and completely clears Odom. Both men have completed their sentences and are on lifelong parole. They are now seeking exoneration in the courts in the hopes of getting on with their lives.

Neither case was part of the Justice Department task force’s review.

A third D.C. case shows how the lack of Justice Department notification has forced people to stay in prison longer than they should have.

Donald E. Gates, 60, served 28 years for the rape and murder of a Georgetown University student based on Malone’s testimony that his hair was found on the victim’s body. He was exonerated by DNA testing in 2009. But for 12 years before that, prosecutors never told him about the inspector general’s report about Malone, that Malone’s work was key to his conviction or that Malone’s findings were flawed, leaving him in prison the entire time.

After The Post contacted him about the forensic issues, U.S. Attorney Ronald C. Machen Jr. of the District said his office would try to review all convictions that used hair analysis.

Seeking to learn whether others shared Gates’s fate, The Post worked with the nonprofit National Whistleblowers Center, which had obtained dozens of boxes of task force documents through a years-long Freedom of Information Act fight.

Task force documents identifying the scientific reviews of problem cases generally did not contain the names of the defendants. Piecing together case numbers and other bits of information from more than 10,000 pages of documents, The Post found more than 250 cases in which a scientific review was completed. Available records did not allow the identification of defendants in roughly 100 of those cases. Records of an unknown number of other questioned cases handled by federal prosecutors have yet to be released by the government.

The Post found that while many prosecutors made swift and full disclosures, many others did so incompletely, years late or not at all. The effort was stymied at times by lack of cooperation from some prosecutors and declining interest and resources as time went on.

Overall, calls to defense lawyers indicate and records documented that prosecutors disclosed the reviews’ results to defendants in fewer than half of the 250-plus questioned cases.

Michael R. Bromwich, a former federal prosecutor and the inspector general who investigated the FBI lab, said in a statement that even if more defense lawyers were notified of the initial review, “that doesn’t absolve the task force from ensuring that every single defense lawyer in one of these cases was notified.”

He added: “It is deeply troubling that after going to so much time and trouble to identify problematic conduct by FBI forensic analysts the DOJ Task Force apparently failed to follow through and ensure that defense counsel were notified in every single case.”

Justice Department spokeswoman Laura Sweeney said the federal review was an “exhaustive effort” and met legal requirements, and she referred questions about hair analysis to the FBI. The FBI said it would evaluate whether a nationwide review is needed.

“In cases where microscopic hair exams conducted by the FBI resulted in a conviction, the FBI is evaluating whether additional review is warranted,” spokeswoman Ann Todd said in a statement. “The FBI has undertaken comprehensive reviews in the past, and will not hesitate to do so again if necessary.”

Santae Tribble and Kirk Odom

John McCormick had just finished the night shift driving a taxi for Diamond Cab on July 26, 1978. McCormick, 63, reached the doorstep of his home in Southeast Washington about 3 a.m., when he was robbed and fatally shot by a man in a stocking mask, according to his widow, who caught a glimpse of the attack from inside the house.

Police soon focused on Santae Tribble as a suspect. A police informant said Tribble told her he was with his childhood friend, Cleveland Wright, when Wright shot McCormick.

After a three-day trial, jurors deliberated two hours before asking about a stocking found a block away at the end of an alley on 28th Street SE. It had been recovered by a police dog, and it contained a single hair that the FBI traced to Tribble. Forty minutes later, the jury found Tribble guilty of murder. He was sentenced in January 1980 to 20 years to life in prison.

Tribble, 17 at the time, his brother, his girlfriend and a houseguest all testified that they were together preparing to celebrate the guest’s birthday the night McCormick was killed. All four said Tribble and his girlfriend were asleep between 2 and 4:30 a.m. in Seat Pleasant.

Tribble took the stand in his own defense, saying what he had said all along — that he had nothing to do with McCormick’s killing.

The prosecution began its closing argument by citing the FBI’s testimony about the hair from the stocking.

This January, after a year-long effort to have DNA evidence retested, Tribble’s public defender succeeded and turned over the results from a private lab to prosecutors. None of the 13 hairs recovered from the stocking — including the one that the FBI said matched Tribble’s — shared Tribble’s or Wright’s genetic profile, conclusively ruling them out as sources, according to mitochondrial DNA analyst Terry Melton of the private lab.

“The government’s entire theory of prosecution — that Mr. Tribble and Mr. Wright acted together to kill Mr. McCormick — is demolished,” wrote Sandra K. Levick, chief of special litigation for the D.C. Public Defender Service and the lawyer who represents Gates, Tribble and Odom. In a motion to D.C. Superior Court Judge Laura Cordero seeking Tribble’s exoneration, Levick wrote: “He has waited thirty-three years for the truth to set him free. He should have to wait no longer.”

In an interview, Tribble, who served 28 years in prison, said that whether the court grants his request or not, he sees it as a final chance to assert his innocence.

“Ms. Levick has been like an angel,” Tribble added, “. . . and I thank God for DNA.”

Details of the new round of hair testing illustrate how hair analysis is highly subjective. The FBI scientist who originally testified at Tribble’s trial, Special Agent James A. Hilverda, said all the hairs he retrieved from the stocking were human head hairs, including the one suitable for comparison that he declared in court matched Tribble’s “in all microscopic characteristics.”

In August, Harold Deadman, a senior hair analyst with the D.C. police who spent 15 years with the FBI lab, forwarded the evidence to the private lab and reported that the 13 hairs he found included head and limb hairs. One exhibited Caucasian characteristics, Deadman added. Tribble is black.

But the private lab’s DNA tests irrefutably showed that the 13 hairs came from three human sources, each of African origin, except for one — which came from a dog.

“Such is the true state of hair microscopy,” Levick wrote. “Two FBI-trained analysts, James Hilverda and Harold Deadman, could not even distinguish human hairs from canine hairs.”

Hilverda declined to comment. Deadman said his role was limited to describing characteristics of hairs he found.

Kirk Odom’s case shares similarities with Tribble’s. Odom was convicted of raping, sodomizing and robbing a 27-year-old woman before dawn in her Capitol Hill apartment in 1981.

The victim said she spoke with her assailant and observed him for up to two minutes in the “dim light” of street lamps through her windows before she was gagged, bound and blindfolded in an hour-long assault.

Police put together a composite sketch of the attacker, based on the victim’s description. About five weeks after the assault, a police officer was talking to Odom about an unrelated matter. He thought Odom looked like the sketch. So he retrieved a two-year-old photograph of Odom, from when he was 16, and put it in a photo array for the victim. The victim picked the image out of the array that April and identified Odom at a lineup in May. She identified Odom again at his trial, telling jurors her assailant “had left her with an image of his face etched in her mind.”

At trial, FBI Special Agent Myron T. Scholberg testified that a hair found on the victim’s nightgown was “microscopically like” Odom’s, meaning the samples were indistinguishable. Prosecutors explained that Scholberg had not been able to distinguish between hair samples only “eight or 10 times in the past 10 years, while performing thousands of analyses.”

But on Jan. 18 of this year, Melton, of the same lab used in the Tribble case, Mitotyping Technologies of State College, Pa., reported its court-ordered DNA test results: The hair in the case could not have come from Odom.

On Feb. 27, a second laboratory selected by prosecutors, Bode Technology of Lorton, turned over the results of court-ordered nuclear DNA testing of stains left by the perpetrator on a pillowcase and robe.

Only one man left all four partial DNA profiles developed by the lab, and that man could not have been Odom.

The victim “was tragically mistaken in her identification of Mr. Odom as her assailant,” Levick wrote in a motion filed March 14 seeking his exoneration. “One man committed these heinous crimes; that man was not Kirk L. Odom.”

Scholberg, who retired in 1985 as head of hair and fiber analysis after 18 years at the FBI lab, said side-by-side hair comparison “was the best method we had at the time.”

Odom, who was imprisoned for 20 years, had to register as a sex offender and remains on lifelong parole. He says court-ordered therapists still berate him for saying he is not guilty. Over the years, his conviction has kept him from possible jobs, he said.

“There was always the thought in the back of my mind . . . ‘One day will my name be cleared?’ ” Odom said at his home in Southeast Washington, where he lives with his wife, Harriet, a medical counselor.

Federal prosecutors declined to comment on Tribble’s and Odom’s specific claims, citing pending litigation.

One government official noted that Odom served an additional 16 months after his release for an unrelated simple assault that violated his parole.

However, in a statement released after being contacted by The Post, Machen, the U.S. attorney in the District, acknowledged that DNA results “raise serious questions in my mind about these convictions.”

“If our comprehensive review shows that either man was wrongfully convicted, we will promptly join him in a motion to vacate his conviction, as we did with Donald Gates in 2009,” Machen said.

The trouble with hair analysis

Popularized in fiction by Sherlock Holmes, hair comparison became an established forensic science by the 1950s. Before modern-day DNA testing, hair analysis could, at its best, accurately narrow the pool of criminal suspects to a class or group or definitively rule out a person as a possible source.

But in practice, even before the “ ‘CSI’ effect” led jurors to expect scientific evidence at every trial, a claim of a hair match packed a powerful, dramatic punch in court. The testimony, usually by a respected scientist working at a respected federal agency, allowed prosecutors to boil down ambiguous cases for jurors to a single, incriminating piece of human evidence left at the scene.

Forensic experts typically assessed the varying characteristics of a hair to determine whether the defendant might be a source. Some factors were visible to the naked eye, such as the length of the hair, its color and whether it was straight, kinky or curly. Others were visible under a microscope, such as the size, type and distribution of pigmentation, the alignment of scales or the thickness of layers in a given hair, or its diameter at various points.

Other judgments could be made. Was the hair animal or human? From the scalp, limbs or pubic area? Of a discernible race? Dyed, bleached or otherwise treated? Cut, forcibly removed or shed naturally?

But there is no consensus among hair examiners about how many of these characteristics were needed to declare a match. So some agents relied on six or seven traits, while others needed 20 or 30. Hilverda, the FBI scientist in Tribble’s case, told jurors that he had performed “probably tens of thousands of examinations” and relied on “about 15 characteristics.”

Despite his testimony, Hilverda recorded in his lab notes that he had measured only three characteristics of the hair from the stocking — it was black, it was a human head hair, and it was from an African American. Similarly, Scholberg’s notes describe the nightgown hair in Odom’s case in the barest terms, as a black, human head hair fragment, like a sample taken from Odom.

Hilverda acknowledged that results could rule out a person or be inconclusive. However, he told jurors that a “match” reflected a high likelihood that two hairs came from the same person. Hilverda added, “Only on very rare occasions have I seen hairs of two individuals that show the same characteristics.”

In Tribble’s case, federal prosecutor David Stanley went further as he summed up the evidence. “There is one chance, perhaps for all we know, in 10 million that it could [be] someone else’s hair,” he said in his closing arguments, sounding the final word for the government.

Stanley declined to comment.

Flaws known for decades

The Tribble and Odom cases demonstrate problems in hair analysis that have been known for nearly 40 years.

In 1974, researchers acknowledged that visual comparisons are so subjective that different analysts can reach different conclusions about the same hair. The FBI acknowledged in 1984 that such analysis cannot positively determine that a hair found at a crime scene belongs to one particular person.

In 1996, the Justice Department studied the nation’s first 28 DNA exonerations and found that 20 percent of the cases involved hair comparison. That same year, the FBI lab stopped declaring matches based on visual comparisons alone and began requiring DNA testing as well.

Yet examples of FBI experts violating scientific standards and making exaggerated or erroneous claims emerged in 1997 at the heart of the FBI lab’s worst modern scandal, when Bromwich’s investigation found systematic problems involving 13 agents. The lab’s lack of written protocols and examiners’ weak scientific qualifications allowed bias to influence some of the nation’s highest-profile criminal investigations, the inspector general said.

From 1996 through 2004, a Justice Department task force set out to review about 6,000 cases handled by the 13 discredited agents for any potential exculpatory information that should be disclosed to defendants. The task force identified more than 250 convictions in which the agents’ work was determined to be either critical to the conviction or so problematic — for example, because a prosecutor refused to cooperate or records had been lost — that it completed a fresh scientific assessment of the agent’s work. The task force was directed to notify prosecutors of the results.

The only real notice of what the task force found came in a 2003 Associated Press account in which unnamed government officials said they had turned over results to prosecutors and were aware that defendants had been notified in 100 to 150 cases. The officials left the impression that anybody whose case had been affected had been notified and that, in any case, no convictions had been overturned, the officials said.

But since 2003, in the District alone, two of six convictions identified by The Post in which forensic work was reassessed by the task force have been vacated. That includes Gates’s case, but not those of Tribble and Odom, who are awaiting court action and were not part of the task force review.

The Gates exoneration also shows that prosecutors failed to turn over information uncovered by the task force.

In addition to Gates, the murder cases in Texas and Maryland and a third in Alaska reveal examples of shortcomings.

All three cases, in addition to the District cases, were handled by FBI agent Malone, whose cases made up more than 90 percent of scientific reviews found by The Post.

In Texas, the review of Benjamin Herbert Boyle’s case got underway only after the defendant was executed, 16 months after the task force was formed, despite pledges to prioritize death penalty cases.

Boyle was executed six days after the Bromwich investigation publicly criticized Malone, the FBI agent who worked on his case, but the FBI had acknowledged two months earlier that it was investigating complaints about him.

The task force asked the Justice Department’s capital-case review unit to look over its work, but the fact that it failed to prevent the execution was never publicized.

In Maryland, John Norman Huffington’s attorneys say they were never notified of the findings of the review in his case, leaving them in a battle over the law’s unsettled requirements for prosecutors to turn over potentially exculpatory evidence and over whether lawyers and courts can properly interpret scientific findings.

In Alaska, Newton P. Lambert’s defenders have been left to seek DNA testing of remaining biological evidence, if any exists, while he serves a life sentence for a 1982 murder. Prosecutors for both Huffington and Lambert claim they disclosed findings at some point to other lawyers but failed to document doing so. In Lambert’s case, The Post found that the purported notification went to a lawyer who had died.

Senior public defenders in both states say they received no such word, which they say would be highly unlikely if it in fact came.

Malone, 66, said he was simply using the best science available at the time. “We did the best we could with what we had,” he said.

Even the harshest critics acknowledge that the Justice Department worked hard to identify potentially tainted convictions. Many of the cases identified by the task force involved serious crimes, and several defendants confessed or were guilty of related charges. Courts also have upheld several convictions even after agents’ roles were discovered.

Flawed agents or a flawed system?

Because of the focus on Malone, many questionable cases were never reviewed.

But as in the Tribble and Odom cases, thousands of defendants nationwide have been implicated by other FBI agents, as well as state and local hair examiners, who relied on the same flawed techniques.

In 2002, the FBI found after it analyzed DNA in 80 selected hair cases that its agents had reported false matches more than 11 percent of the time. “I don’t believe forensic science truly understood the significance of microscopic hair comparison, and it wasn’t until [DNA] that we learned that 11 percent of the time, two hairs can be microscopically similar yet come from different people,” said Dwight E. Adams, who directed the FBI lab from 2002 to 2006.

Yet a Post review of the small fraction of cases in which an appeals court opinion describes FBI hair testimony shows that several FBI agents gave improper testimony, asserting the remote odds of a false match or invoking bogus statistics in the absence of data.

For example, in testimony in a Minnesota bank robbery case, also in 1978, Hilverda, the agent who worked on Tribble’s case, reiterated that he had been unable to distinguish among different people’s hair “only on a couple of occasions” out of more than 2,000 cases he had analyzed.

In a 1980 Indiana robbery case, an agent told jurors that he had failed to tell different people’s hair apart just once in 1,500 cases. After a slaying in Tennessee that year, another agent testified in a capital case that there was only one chance out of 4,500 or 5,000 that a hair came from someone other than the suspect.

“Those statements are chilling to read,” Bromwich said of the exaggerated FBI claims at trial.

Todd, the FBI spokeswoman, said bureau lab reports for more than 30 years have qualified their findings by saying that hair comparisons are not a means of absolute positive identification. She requested a list of cases in which agents departed from guidelines in court. The Post provided nine cases.

Todd declined to say whether the bureau considered taking steps to determine whether other agents intentionally or unintentionally misled jurors. “Only Michael Malone’s conduct was questioned in the area of hair comparisons,” Todd said. “The [inspector general] did not question the merits of microscopic hair comparisons as a scientific discipline.”

Experts say the difference between laboratory standards and examiners’ testimony in court can be important, especially if no one is reading or watching what agents say.

“It seemingly has never been routine for crime labs to do supervision based on trial testimony,” said University of Virginia School of Law professor Brandon L. Garrett. “You can have cautious standards, but if no one is supervising their implementation, it’s predictable that analysts may cross the line.”

‘Veil of secrecy’

A review of the task force documents, as well as Post interviews, found that the Justice Department struggled to balance its roles as a law enforcer defending convictions, a minister of justice protecting the innocent, and a patron and practitioner of forensic science.

By excluding defense lawyers from the process and leaving it to prosecutors to decide case by case what to disclose, authorities waded into a legal and ethical morass that left some prisoners locked away for years longer than necessary. By adopting a secret process that limited accountability, documents show, the task force left the scope and nature of scientific problems unreported, obscuring issues from further study and permitting similar breakdowns.

“The government has hidden behind the veil of secrecy to shield these abuses despite official assurances that justice would be done,” said David Colapinto, general counsel of the National Whistleblowers Center.

The American Bar Association and others have proposed stronger ethics rules for prosecutors to act on information that casts doubt on convictions; opening laboratory and other files to the defense; clearer reporting and evidence retention; greater involvement by scientists in setting rules for testimony at criminal trials; and more scientific training for lawyers and judges.

Other experts propose more oversight by standing state forensic-science commissions and funding for research into forensic techniques and experts for indigent defendants.

A common theme among reform-minded lawyers and experts is taking the oversight of the forensic labs away from police and prosecutors.

“It’s human to make mistakes,” said Steven D. Benjamin, president-elect of the National Association of Criminal Defense Lawyers. “It’s wrong not to learn from them.”

More specifically, the D.C. Public Defender Service, Benjamin’s group and others said justice would be served by retesting hair evidence in convictions nationwide from 1996 and earlier. “If microscopic hair analysis was a key piece of evidence in a conviction, and it was one of only a limited amount of evidence in a case, would it be worthwhile to retest that using mitochondrial DNA? I would say absolutely,” said Adams, the former FBI lab director.

The promised review by federal prosecutors of hair convictions in the District would not include cases before 1985, when FBI records were computerized, and would not disclose any defendant’s name. That approach would have missed Gates, Odom and Tribble, who were convicted earlier.

Representatives for Machen, the FBI and the Justice Department also declined to say why the review should be limited to D.C. cases. The Post found that 95 percent of the troubled cases identified by the task force were outside the District.

Avis E. Buchanan, director of the D.C. Public Defender Service, said her agency must be “a full participant” in the review, which it has sought for two years, and that it should extend nationwide. “Surely the District of Columbia is not the only place where such flawed evidence was used to convict the innocent,” she said.

Staff researcher Jennifer Jenkins and database editor Ted Mellnik contributed to this report.