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Mary Altaffer, File, Associated Press
FILE- In this March 23, 3016 file photo, Richard Rosario, center, and his lawyers Glenn Garber, right, and Rebecca Freedman, of the Exoneration Initiative, listen as a judge sitting in New York overturns Rosario's conviction. Rosario, who spent 20 years in prison for a killing he says happened while he was in Florida, asked a judge on Friday, June 24, 2016 to keep his case open so he could be fully vindicated.

NEW YORK — After 20 years behind bars for a murder he says he didn't commit, Richard Rosario was about to get the charges dropped Friday. Until he said no.

Prosecutors conceded he'd been wrongfully convicted and said they would dismiss the charges because they felt they couldn't retry the 1996 case. But in a highly unusual move, Rosario persuaded a court to leave the case open for more investigation, saying prosecutors should fully exonerate him, not just end the case.

"It's not acceptable. The public should know the truth," said Rosario, who told police early on that 13 people could vouch that he was in Florida when Jorge Collazo, also called George Collazo, was killed on a Bronx street. "It's clear that I'm innocent."

Surprised, Bronx state Supreme Court Justice Robert Torres agreed to leave the case open at least through Aug. 30, over objections from prosecutors who said they had already robustly reinvestigated the killing.

Rosario had been freed in March after new Bronx District Attorney Darcel Clark agreed Rosario had been improperly convicted because his former defense attorneys hadn't done enough to track down Rosario's alibi witnesses. Clark didn't immediately dismiss the charges in March, saying she needed more time to reinvestigate.

Prosecutors considered the evidence they could produce, the alibi witnesses and the time Rosario had served, and they concluded they couldn't prove the case at trial, said Julian Bond O'Connor, Clark's deputy counsel.

"This office is and remains fully committed to investigating and making every single effort to find and prove what happened that day," but the indictment shouldn't hang over Rosario, O'Connor said.

But Rosario said he'd rather live with the indictment than with a resolution that didn't vindicate him.

"All I'm seeking is transparency for me and my family, for the community and for the victim's family," he said.

Collazo's relatives bristled at Rosario's insistence that he should be cleared.

"You were never proven innocent. Let's just get it straight," the victim's father and namesake said, approaching Rosario outside court.

The father said he didn't take issue with overturning Rosario's conviction because of the questions about his defense, but "there's a lot of deception" in arguments for Rosario's innocence.

The case, which has been featured in a "Dateline" digital series on NBCNews.com, is among more than 25 convictions from New York City's high-crime 1980s and '90s that prosecutors have disavowed in the last five years.

Rosario's attorneys have called his case an illustration of unreliable eyewitness testimony, bungled defense and the difficulty of fighting a guilty verdict. He had lost multiple appeals over the years.

Rosario was arrested after two witnesses identified him from a police photo book as the man who'd shot the 17-year-old Collazo in the head after an exchange of words on a street on June 19, 1996. No forensic or physical evidence tied Rosario to the crime.

He said he'd been staying with friends in Deltona, Florida, and he listed over a dozen people he said had seen him there.

Police didn't contact those people, according to Rosario's current lawyers. And his own court-appointed attorneys at the time didn't fully explore the alibi witnesses, either.

After phoning the witnesses proved difficult, his first attorney got a judge's OK to pay to send a private investigator to Florida but then never dispatched the investigator, according to a 2010 appeals court decision. Another defense lawyer took over before Rosario's trial and mistakenly thought the court had nixed funding for the investigator's Florida trip.

Some of the witnesses did testify at trial, but prosecutors at the time urged jurors to discount them because they were Rosario's friends.

During Rosario's appeal, a judge said additional alibi witnesses wouldn't have added significantly to his defense. Rosario's lawyers argue otherwise.

Reach Jennifer Peltz on Twitter @ jennpeltz.