The police did not respond to a request for comment on the district attorney’s report.
Irving Cohen, Mr. Williams’s lawyer for the last seven years, said that it was all too typical for police detectives at that time to stop investigating once they identified a suspect. He said he had handled about 15 similar cases dating to the late 1980s and the 1990s, and that the pressure on investigators to clear cases was often at play.
Back then, if cases like Mr. Williams’s were reinvestigated at all, such reviews were usually undertaken on an ad hoc basis by district attorneys responding to claims of innocence from defendants and their lawyers.
But over the past decade, conviction review units like the one that reinvestigated Mr. Williams’s case have become far more common, thanks in part to Kenneth P. Thompson, the Brooklyn district attorney between 2014 and 2016, whose office exonerated more than 20 people it found had been wrongfully convicted.
Not all conviction review units, or conviction integrity units, are alike, and some have been criticized for a lack of transparency, for existing “in name only,” or for being staffed solely by prosecutors, who do not always have strong incentives to overturn their colleagues’ work.
Still, conviction integrity units, as well as pressure from outside organizations like the Innocence Project and others, have led to more exonerations over the past several years.
Many involve trials like Mr. Williams’s, where evidence appears to have been scant. Prosecutors at his trial, in November 1997, placed special emphasis on the Wu-Tang hat, noting that Mr. Williams had been employed at the Wu-Tang recording studio. But the Wu-Tang Clan, the most famous rap group from Staten Island, would have been near the height of its popularity that year.
(Later, from prison, Mr. Williams asked that the hat be tested for DNA evidence, but it had been destroyed by the police, as was their standard procedure.)