Years after the verdict, a conviction for a 2003 murder appeared to be under threat.

An assistant district attorney, according to court filings, had discovered that trial prosecutors hid evidence undermining the credibility of testimony that Lavar Brown was an accomplice to the murder of North Philadelphia Rite Aid manager Michael Richardson. The lawyer learned that one of two witnesses who testified against Brown had falsely implicated a woman who was incarcerated at the time of the murder and the lie wasn’t disclosed.

Then, according to the filing, prosecutors decided to continue the cover-up.

Lawyers for the Philadelphia DA’s Conviction Integrity Unit (CIU) now say that a review of the case file revealed a “pattern of prosecutorial misconduct” and that Brown should get a new trial.

“Those documents not only paint a picture of an unfair trial, they also reveal the equally problematic actions of post-conviction prosecutors scrambling to maintain a conviction despite the clearly questionable conduct of the trial prosecutors,” the CIU lawyers wrote in a Nov. 1 filing in Philadelphia Common Pleas Court.

The filing included an internal DA’s Office email in which a supervisor described concealing prior witness statements as both routine and acceptable, and even proposing retaliation against a defense lawyer who provided information helpful to Brown.

» READ MORE: Philly's exonerations, rife with allegations of misconduct, call decades of homicide investigations into question

The prosecutors who worked on the case insist they acted properly.

Trial prosecutor Tom Malone said in a statement that it was “appalling” that the DA’s Office would move to reverse Brown’s conviction, noting that there was ample evidence of Brown’s guilt and that he is on death row for a second murder, the killing of Robert Crawford. (He also said District Attorney Larry Krasner had a pattern of trying “to usurp the role of the courts” to help Brown by agreeing that Brown should be resentenced to life for the Crawford murder. The Pennsylvania Supreme Court rejected that.)

And the victim’s widow, Kristi Richardson, has sought to intervene, saying it’s Krasner’s administration that is committing the injustice. She said the DA waited until the last minute to notify her of a November court date at which the CIU agreed Brown was owed a new trial.

She also alleged that Krasner has a conflict of interest because his former business associates were previously connected to the case. One of them, Lloyd Long, represented Brown on a post-conviction petition; another, Jamie Funt, represented one of the unindicted coconspirators and was a witness at a post-conviction hearing.

“They had 17 months to call the wife of the murder victim,” said Guy D’Andrea, who said he is representing Richardson pro bono. “Why did they call her 11 hours before the court date?”

Cari Mahler, the assistant DA who handled the case during a 2010 post-conviction hearing, said in an email that no exculpatory evidence was withheld. “The evidence overwhelmingly established that Lavar Brown was the mastermind behind the robbery plot that resulted in the victim’s brutal murder,” she said.

She accused the DA’s Office of improperly disclosing internal communications and seeking to circumvent the judiciary rather than hold a complete adversarial hearing.

Brown was one of four people convicted of Richardson’s murder, a plot in which Christopher Kennedy was supposed to shoot the store manager in the leg but ended up shooting him in the head. Kennedy was caught fleeing the store with a gun and cash. Brothers James and Jamaar Richardson, who admitted to roles in the robbery, were also convicted. (They are not related to Michael Richardson.)

The case against Brown was the thinnest of the group, according to the CIU: He was convicted based only on the testimony of two unindicted coconspirators. The CIU now says trial prosecutors hid the fact that one of them, Kyonna Lyons, had given a previous, conflicting statement to Malone and Detective David Baker. Baker and Malone, according to the DA’s filing, said they didn’t document that statement because they believed she was lying. The CIU said the trial prosecutors also hid that the other informant, Ronald Vann, had cooperated in multiple cases and had lied in his statement on the Rite Aid case by falsely implicating an additional person.

Malone said the CIU did not give him the opportunity to review the file but added, “I am confident that their representation about exculpatory evidence is false.”

When the information about Lyons’ prior statement came to light, prosecutors debated how to proceed. In a 2010 email to his colleagues, included in the DA’s court filings, then-homicide unit deputy chief Ed Cameron said the omissions were acceptable.

» READ MORE: The battle in Philly DA’s Office: Conviction Integrity Unit report shows rocky path to reform

“We never advise defense attorneys about [prior inconsistent statements],” wrote Cameron, who died last year. He said the “only issue is” that Brown’s lawyers found out. He even suggested retaliating against Lyons’ lawyer, Funt: “If Funt is going to come in and say things to hurt us, we should not give him deals in the future. Also, maybe we should send a detective to go interview him.”

That Brown will remain on death row no matter the outcome of this case, CIU supervisor Patricia Cummings said, did not factor into the decision to agree to a new trial. “When we have evidence of this kind of misconduct, you have to act on it,” she said. “He didn’t get a fair trial, period.”

The U.S. Supreme Court has repeatedly affirmed that prosecutors must disclose evidence favorable to a defendant — including evidence that may cast doubt on the integrity of a witness. R. Michael Cassidy, a professor of law specializing in prosecutorial ethics at Boston College, said evidence that witnesses lied falls squarely into that disclosure requirement.

» READ MORE: ‘Lying now, or lying then?’ Under Pa. rules, many are convicted on recanted statements.

Police, he said, have often avoided writing down contradictory statements so they would not have to disclose them, he said. “That is completely inconsistent with the Supreme Court precedent. It doesn’t matter if the statement is oral or written. That’s impeachment material that the other side is entitled to know about.”

In Brown’s case, the court has not yet determined whether to accept the DA’s agreement to a new trial — or decided whether to act on Richardson’s request to conflict the DA out of the case, or have him removed because of a conflict of interest.

Cassidy said there might be a basis for the allegation that Krasner has a conflict under Pennsylvania’s rules of professional conduct. The rule bars a lawyer from representing a client if doing so would conflict with a personal interest — in this case, Krasner’s loyalty to his ex-partner. But, Cassidy added, he believes such a claim is unlikely to succeed, especially because courts have traditionally been reluctant to conflict out government lawyers.

Cummings said there is no conflict, because Funt’s and Long’s involvement ended before either worked with Krasner. A Krasner spokesperson declined to provide a written conflict policy but said all relevant cases are referred to the DA’s chief ethics officer for a “rigorous conflicts screening process.”

It will be up to Common Pleas Court Judge Scott DiClaudio, who repeatedly sparred with Krasner after the DA unsuccessfully sought to have him removed from criminal court over his own purported conflict. (DiClaudio’s then-girlfriend had filed an employment discrimination complaint against the DA’s Office.)

DiClaudio scheduled a hearing for December on whether to remove the case from the DA’s Office and refer it to the attorney general. He asked Krasner to testify.

“It makes sense for him to explain in open court to the widow that his office should be making a decision in his ex-partner’s cases,” DiClaudio said in court.

Cummings called the conflict question a distraction from the larger issues raised by the case: “It really does potentially call into question homicide convictions where cooperators were used. We know that the cops have lied and cheated for a long time ... but in this case you have for the first time documentation of the extent to which prosecutors were playing this game, as well.”