In an extraordinary step, the Philadelphia District Attorney's Office on Tuesday pointed an accusatory finger at onetime members of its own office, asserting in a court motion that police and prosecutors helped to convict a city man of murder a decade ago by "hiding" evidence that suggested he was innocent, possibly breaking the law in the process.

For the first time, prosecutors say they believe Dontia Patterson is innocent, something Patterson had maintained for 11 years behind bars. Calling Patterson's conviction "an egregious example of police and prosecutorial misconduct," the motion, signed by Anthony Voci, the office's chief of homicide, suggests that two former prosecutors may have acted in bad faith because they knew they couldn't otherwise win the case.

It also says that Patterson's case file contained information that pointed to a more likely shooter, a man murdered about two months after his arrest and just blocks from the shooting Patterson was accused of committing.

The document is likely to lead to the exoneration of Patterson, 29, and could resonate beyond his case as the most stinging rebuke yet of Philadelphia's criminal justice system by its current top prosecutor, Larry Krasner.

One of the targets of the motion's allegations, former homicide prosecutor Richard Sax, in an interview Tuesday night slammed the decision to back Patterson's exoneration as "a horrific travesty of justice." Jurors had decided he was guilty beyond a reasonable doubt, Sax said, and an appeal effort was denied.

Sax, a vocal critic of Krasner since the campaign trail, said he had not withheld information that could have been helpful to Patterson. He said he thought the case was being overturned in part because of bad blood between himself and the district attorney.

"To have a political [dismissal] because the district attorney really doesn't like the second of two prosecutors who tried the case is horrific," Sax said.

Krasner, a self-described reformer who took office in January, made no secret as a candidate of his disdain for what he considered a win-at-all-costs mentality among Philadelphia prosecutors. And the motion — filed by his office in Patterson's still-pending case — does not hold back in its assessment of Sax and former Assistant District Attorney Beth McCaffery, although neither is named in the document.

Patterson's prosecution, the motion says, was "illogical" and "completely lacking in integrity." Not only was Patterson improperly imprisoned, it says, but the victim's family was given a false sense of closure and the public was ill-served when the likely shooter remained on the streets until he was killed.

Sax said that the case against Patterson "was not weak" and that two witnesses identified him and a jury voted to convict him. He said Krasner's office was looking at the case "in the light most favorable to the defense," rather than applying the law properly.

"It seems like they took this opportunity to argue as hard as they could for everything that could possibly be said on behalf of the defendant," he said. "And that's not what prosecutors are supposed to do."

Patterson's conviction was vacated in February after prosecutors agreed his defense attorney was ineffective. He has been on house arrest since last month and is due back in court Wednesday, when prosecutors will ask a judge to sign off on Voci's decision to drop all remaining charges.

Patterson was accused of fatally shooting his friend Antwine Jackson, 18, on Jan. 11, 2007, outside a corner store on the 800 block of Granite Street. His first trial, in 2008 — handled by McCaffery — ended in a hung jury. He was retried the following year by Sax and convicted of first-degree murder.

Attempts to reach McCaffery for comment Tuesday night were unsuccessful.

No motive for the killing was ever determined, Voci's motion says, and no physical evidence connected Patterson to the crime. The case rested largely on two eyewitnesses about 40 yards from the store, the motion says.

Voci said that information about alternate suspects was not turned over to the defense before either trial, and that prosecutors at the time also failed to disclose potentially damning information against another witness who testified at Patterson's second trial.

Deliberately withholding evidence from a defendant, the motion says, "is not law enforcement in any sense — it is a violation of the law." Courts have held that prosecutors must share all relevant evidence, even if it may be favorable to a defendant.

Although the motion does not explicitly accuse either McCaffery or Sax of intentional misconduct, it does say it was "inconceivable" that either was unaware of the exculpatory evidence, and later says, "Without concealment of exculpatory evidence, the prosecution could not win."

Sax said: "Everything that was either exculpatory or arguably exculpatory was turned over. That's without any question." He also said he felt "horrible" for Jackson's relatives. Attempts to reach them for comment Tuesday night were unsuccessful.

Hayes Hunt, Patterson's appellate attorney, said in an email Tuesday that he was grateful that prosecutors were "righting this great wrong." Hunt, of the Center City firm Cozen O'Connor, worked pro bono on the case with the Pennsylvania Innocence Project.

"Mr. Patterson's conviction for murder undermines the credibility of our criminal justice system and is Exhibit A for reform and thoughtful change in Philadelphia," Hunt said. "His prosecution was an indictment against due process and basic fairness."

Marissa Bluestine, executive director of the Pennsylvania Innocence Project, said in an interview that Patterson was "very emotional, overwhelmed" by Tuesday's news.

"He spent 11 years locked in a cell where everything was dictated for him," Bluestine said, "and he knew that he didn't belong there."