Fueled by the freeing of a prison inmate who claimed a detective framed him in a 1990 murder, the Brooklyn district attorney’s office has undertaken one of the nation’s most ambitious efforts to revisit cases of people put behind bars decades ago to determine whether they were wrongly convicted.

District Attorney Kenneth Thompson is re-examining about 90 mostly homicide cases from the 1980s and 1990s — an era when New York City’s murder rate was soaring — including nearly 60 cases linked to the same detective. While other prosecutors’ offices have also launched such projects, exoneration experts say few, if any, have tackled such a sweeping examination all at once.

“No one else is dealing with this type of volume,” said Samuel Gross, a professor at the University of Michigan Law School who heads the National Registry of Exonerations. “They’re starting out on a long journey, and they don’t know where it will take them.”

Thompson, who took office in January, is accelerating an effort started by his predecessor, increasing the number of prosecutors dedicated to the project from three to 10, hiring a Harvard Law School professor to guide the unit and appointing a panel of experienced lawyers to give their outside, volunteer input. He told a City Council budget committee last week that the annual cost will top $1 million.

“These actions not only foster public trust in the criminal justice system but also begin the process of righting an injustice committed against these defendants,” Thompson said.

Elsewhere, Dallas County District Attorney Craig Watkins started a pioneering conviction-integrity unit that has cleared more than 30 people since 2007. Next door to Brooklyn, Manhattan District Attorney Cyrus R. Vance Jr.’s office has examined more than 150 cases, extensively reinvestigated 12 and exonerated four people since 2010. Similar efforts are underway in DA’s offices from San Jose, California, to Utica, New York.

In Brooklyn, prosecutors so far have persuaded judges to throw out six convictions this year, including those of three half brothers who were found guilty in two fatal shooting cases that relied on faulty eyewitness testimony from a crack addict. More dismissals are expected, but those spearheading the inquiries caution that the process can be a complex voyage back in time.

Witnesses are difficult to locate. So are decades-old court records. Lab work isn’t an option because there’s no DNA evidence.

In recent months, defendants, their lawyers and relatives, and even the DA’s office’s own appeals bureau have contacted the unit about potential wrongful convictions. The unit has sought to prioritize the cases by first looking at viable claims of innocence, as opposed to trial errors, made by defendants still in prison, said Eric Gonzalez, who oversees the effort.

The bulk of the cases — 57 — stem from concerns about the investigative tactics of now-retired New York City police detective Louis Scarcella.

New evidence that Scarcella coached a witness to pick a suspect out of a lineup led to the exoneration last year of a man who served 23 years in prison for the slaying of a Brooklyn rabbi.

That decision sparked renewed allegations that Scarcella fabricated confessions, manipulated witnesses and intimidated suspects in other cases — charges he denies.

At a recent City Hall rally, convicts who have completed lengthy sentences in cases investigated by Scarcella complained the process is moving too slowly and worry their names will never be cleared.

“I feel violated, humiliated,” said Derrick Hamilton, who served 21 years for a slaying he says he didn’t commit. “How long must we wait for justice?”