A rape conviction from nearly 40 years ago involving best-selling author Alice Sebold was overturned last week after the authorities determined that the 1982 conviction was flawed because it relied on a forensic technique that has since been debunked: microscopic hair analysis.

Anthony J. Broadwater, now 61, spent 16 years in prison after he was convicted of raping Sebold when she was a student at Syracuse. Sebold wrote about the assault and the post-traumatic stress disorder she suffered in her 1999 memoir, “Lucky.” A follow-up novel, “The Lovely Bones,” was a bestseller that was adapted as an award-winning film.

Broadwater consistently maintained his innocence, undergoing two polygraph tests while serving his sentence. The rape kit used in the case was destroyed before D.N.A. testing was available. But in 2019 a producer working on a film adaptation of “Lucky” noticed discrepancies between Sebold’s account and testimony at trial. Only then was the question of Broadwater’s guilt taken seriously.

According to Syracuse.com, which first covered the exoneration, two pieces of evidence were critical to Broadwater’s exoneration. The first was Sebold’s failure to identify Broadwater in a police lineup. The other was a strand of hair.

A Retro Report video, “Flawed Evidence: The Limits of Science in the Crime Lab,” above, looks at the pseudo-science behind hair analysis, a technique that dominated forensics for decades. Hair analysis was discredited in 1996, but many people whose convictions hinged on hair analysis remain in prison today.

Before D.N.A. testing was introduced in the late 1980s, forensic science relied on analyzing strands of hair. Hair analysis, which had been explored in the 1850s and became a widely established forensic tool by the 1950s, relied on visual observation of hair samples under high-powered microscopes. Forensic scientists used visual indicators like pigment or scale patterns to match hair from a defendant to samples collected from a crime scene. The F.B.I.’s hair and fiber laboratory became an essential part of its investigations, and in criminal court proceedings, hair analysis was often presented to juries as undeniable forensic evidence.

In 1981, a year before Broadwater was convicted, Kirk Odom was convicted of rape, with hair analysis playing a key role. Odom’s accuser identified him in a lineup, but her identification was later called into question. Police found one hair on the victim’s nightgown, which F.B.I. analysts determined was microscopically similar to Odom’s hair. A later investigation uncovered F.B.I. laboratory notes that revealed the hair was only identified by color and type of body hair. Odom served more than 20 years in prison.

The first exoneration based on mitochondrial D.N.A. evidence occurred in 1989. In the early 90s, the Innocence Project, a nonprofit organization committed to exonerating wrongfully convicted individuals through D.N.A. testing, started retesting crime scene evidence. By 2012, the group found that in 300 exonerations, nearly 25 percent of the convictions hinged on hair analysis.

Three high-profile exonerations made headlines in 2012 as part of a major Washington Post investigation into flawed hair testimony. One of the defendants was Kirk Odom, who, since his release in 2003, had been living as a registered sex offender. The bombshell report forced the F.B.I. to take a fresh look at past cases.

By 2015, the government identified 3,000 cases in which F.B.I. examiners submitted testimony using microscopic hair analysis. A review by the Justice Department, the Innocence Project and the F.B.I. showed that of 268 cases, 96 percent contained erroneous statements and exaggerated matches of hair samples. At least 35 defendants convicted using hair analysis had been sentenced to death.

In recent interviews, Broadwater has detailed the difficulties of life after prison, especially with the stigma of being a registered sex offender. On Tuesday, Sebold acknowledged her role in perpetuating a racial injustice.

“I will remain sorry for the rest of my life that while pursuing justice through the legal system, my own misfortune resulted in Mr. Broadwater’s unfair conviction for which he has served not only 16 years behind bars but in ways that further serve to wound and stigmatize, nearly a full life sentence,” she wrote.

According to the Innocence Project, 45 percent of wrongful convictions are based on misapplied forensic evidence, including bite marks and smudged fingerprints. Time limits can make it difficult for convicted people to be exonerated, but several states have reformed statute of limitations laws, making it easier for these individuals to challenge their cases based on new scientific evidence.

At Broadwater’s hearing, the Onondaga district attorney, William Fitzpatrick, vowed never to let a conviction like Broadwater’s happen again. “I’m not going to sully this proceeding by saying I’m sorry. That doesn’t cut it,” he said. “I will say to Mr. Broadwater, that I assure him that it will never happen again. That we will never let junk science into a courtroom in this county.”

ANNY OBERLINK, an intern at Retro Report, is a degree candidate in documentary filmmaking at CUNY’s Craig Newmark Graduate School of Journalism. This article first appeared in Retro Report’s free weekly newsletter. Subscribe and receive lessons from history in your mailbox. Follow us on Twitter @RetroReport.