This piece was written and produced by NY1 Assignment Editor Nicole Porette as part of the 2015 John Jay/H.F. Guggenheim fellowship on race, crime, and justice.

On a typical evening more than 30 years ago, Johnnie O'Neal was home watching television with his family. At the same time that night on March 16, 1984, a brutal crime was being committed in the Douglass Houses in Manhattan -- one that would change O'Neal's life forever. The victim in that assault, a 21-year-old woman, was robbed and raped at knifepoint. 

In the aftermath, the woman, along with her mother, would later identify O'Neal as the assailant. He was charged with rape and robbery, and later convicted and sentenced to 10 to 20 years in prison.

"I didn't see any hope for me," said O'Neal.

The arrest and the subsequent quest by O'Neal, who maintained his innocence, to prove that he didn't commit the crimes are not uncommon. But an initiative used by some district attorneys -- and which eventually was crucial in the outcome of O'Neal's case -- is gaining traction nationwide.

But O'Neal, who was repeatedly denied parole, served 13 years in prison for the rape and robbery. And in the years that followed, O'Neal continued to fight to prove his innocence, especially for his mother's sake.

"You know she wore the stigma that her son was a rapist," he said, "and that just killed me."

Eight years after his release lawyers from the Legal Aid Society filed a motion to have O’Neal dropped from a Level 3 to a Level 1 sex offender. During that time the attorneys began reinvestigating his case, and reinterviewed the victim and her mother in 2008. 

They recanted their story about where they saw O'Neal and when, and the lawyers' investigation revealed other inconsistencies with the victim’s original story.

That cleared the way in 2010 for O’Neal to contact the Manhattan District Attorney’s Conviction Integrity Unit to request that his case be given a second look. The Manhattan DA conducted its own investigation and in 2013 filed a motion supporting O'Neal's lawyers' motion to dismiss the charges.

And after more than 28 years, O’Neal finally had his name cleared.

O'Neal's current attorney, Jason Leventhal, says it may never have happened if the Manhattan District Attorney didn't have a dedicated unit to review cases like this. 

"The creation of a conviction integrity unit is a model that every prosecutor's office should follow," he said.

O’Neal’s case is just one example of the 1,600 exonerations that have occurred since 1989, according to the National Registry of Exonerations (NRE). 

Several District Attorneys’ offices across the country have created Conviction Integrity Units (CIU) to investigate post conviction claims of innocence. According to the NRE, as of March 2015 there were 15 CIUs in the U.S. In New York City, Manhattan and Brooklyn are the only districts to have launched units.

The men in charge of those offices happen to be two of the newer district attorneys. Manhattan DA Cyrus Vance has been in office for five years, and in Brooklyn, Ken Thompson has been in office for only a year and a half.

Vance created the first such unit in the city in 2010. He says one goal in creating the unit was to be more transparent about how his office deals with issues of conviction integrity. 

"We need to make sure that we are doing the best we can to avoid making error judgments at the beginning of a case that may lead to a wrongful conviction," Vance said. "And we need to have a process post conviction where people or lawyers believe their case should be reviewed."

Manhattan's unit is currently comprised of 10 senior members who are trained in the process of reviewing and re-investigating cases. Vance has recently requested funding to add another attorney to the staff. So far the unit has reviewed more than 160 cases involving serious felonies such as homicides, rapes, burglaries, and robberies. They went on to re-investigate 14 of those cases and O'Neal's case is one of five that the office has consented to vacate.

Vance also has a separate advisory panel comprised of criminal justice experts such as former judges, former prosecutors, professors, and defense attorneys who advise the office on the best practices for reviewing cases. 

"Outsiders are important because they can provide experience and input on what they think about the work we're doing and how we can do it better," he says.

In Kings County, former District Attorney Charles Hynes created the unit in 2011. Two years later, Hynes created a separate panel to review cases involving a former NYPD detective named Louis Scarcella after a review by the New York Times found the detective used the same witness in several cases. 

Hynes said at the time that the investigations of a 1991 murder case Scarcella worked on "revealed allegations of improprieties on the part of the investigative detective, Louis Scarcella." 

After his election in 2014, Thompson expanded the office's unit, which is now referred to as the Conviction Review Unit. It is comprised of 10 assistant district attorneys and three investigators, including former homicide prosecutor Mark Hale. Most of the units investigations are into cases that Scarcella worked on. During Thompson's first year the unit successfully overturned 10 murder convictions for defendants who were wrongfully incarcerated due to Scarcella's actions.

The Conviction Review Unit has taken on the task of investigating more than 70 convictions in which Scarcella was involved in the initial investigation. The cases focus mostly on human error, which can prove harder to investigate than cases involving DNA, Hale says. 

"It is more of a challenge but it is more of an exacting examination then has been done anywhere in country by anybody," he said. "We're looking at everything, reexamination of witnesses, conduct of police officers, conduct of prosecutors even the performance of the defense attorney so that we can get a total picture not just one slice of it like the DNA cases are."

Hale also admits there are some difficulties when investigating crimes that happened so far in the past and not relying on DNA evidence. 

"Things are different now, prosecutions now are based in large part on DNA evidence, on social media on videotaped cameras that seem to be on every corner now that certainly weren't there 10, 15 years ago going before that when prosecutions were basically built on confessions and eyewitness observations as opposed to scientific evidence and documentary evidence," he said.

Brooklyn’s Conviction Review Unit is praised as one of the best in the country. Since 2014 it has investigated and vacated convictions for 13 individuals. Hale says a big part of the success was Thompson's decision to have former Defense Attorney and Harvard Professor Ron Sullivan revamp the unit. 

Hale says Sullivan "has studied all the various conviction review units around the country to try and establish here what we felt was the best practices and best standards to look at these cases."

Barry Shceck, co-founder of the Innocence Project, a nonprofit that litigates cases involving wrongfully incarcerated individual, stresses the importance of prosecutors working with defense attorneys like Sullivan.  

"I think that the best practice for a conviction integrity unit that's proven to be a success in both Dallas and now in Kings County Brooklyn the first step is there has to be a defense lawyer, former defense lawyer, and you make them a person with high level supervisor responsibility for the unit," he said. "The reason that's true is we all have these biases that arise when we work within an institution and just by saying tomorrow you're going to review all the cases of your colleagues and the conviction integrity unity, for somebody that's been a prosecutor for 20-30 years, that's a hard job no matter how fair minded you are because you just look at the cases different."

Although the city's other three District Attorneys office do not have dedicated units to investigate possible wrongful convictions, they say they do have systems in place for either preventing or investigating possible wrongful conviction claims.

In 1996 Queens District Attorney Richard Brown created the Felony Waiver/No Plea Policy. This policy allows the defendant and his attorney to meet with prosecutors and weigh the strengths and weaknesses of the evidence before a criminal arraignment. 

"It is this process and those discussions which, at the earliest date, will lead to the most thorough and comprehensive investigation possible and will most likely exonerate an innocent defendant," said Queens DA spokesman Kevin Ryan, who added that the goal was to prevent wrongful convictions before they happen.

Ryan says when there is the possibility of a wrongful conviction it is re-investigated by members of the office's executive staff and they report their findings directly to Brown. There have been 12 defendants who have had their cases re-investigated to have their charges dismissed. Of the 12 investigations, only one was commenced as a result of information gathered.

On Staten Island, the Richmond County District Attorney says its office investigates claims of innocence when a post judgment claim of innocence in the form of a letter or motion is filed with the court. Once that is done, the Chief of the Appeals Bureau reviews the case and discusses his or her findings with executive ADA and Chief ADA before briefing the District Attorney on the matter. So far no convictions have been overturned there based on a case being reviewed using that procedure. 

The Bronx District Attorney’s office also does not have a unit dedicated to re-investigating previous convictions but says it will review cases when issues are brought to their attention. There have been 10 defendants over the past 10 years who have had their convictions overturned after the office filed motions to vacate their convictions. 

Hale, meanwhile, says the important part of having a dedicated unit is that the offices are acknowledging they are not always perfect. 

"If you're honest with yourself as a prosecutor your job is to do justice and not just secure a conviction," he said. "And if your job is to do justice you have to recognize that as human beings we may have made mistakes."

Scheck, who works with DAs across the country, says it's important for DAs to realize the need for specialized units that review allegations of wrongful convictions. 

"There are a number of district attorney offices that will say ‘We have a conviction integrity unit’ but you can tell by the best practices that they don’t follow that they are not serious because they're not exchanging information with the defense. The people they're putting in there don’t have defense backgrounds, are not looking at the cases without institutional blinders, there's much to be learned from this process and it is important to do it right," he said. "I would certainly hope that very soon our colleagues in The Bronx and Staten and Queens would go through the processes and figure out how do we put up a conviction integrity unit...nothing is more important."

As for O'Neal, he says although his conviction has been overturned, he still lives with the stigma of being labeled a rapist. 

"To be categorized as one," he said, "is like a death sentence."