Imprisoned hip-hop star Meek Mill has opened a new avenue of appeal, focusing on recent revelations that a key witness in his case is one of several police officers that the Philadelphia District Attorney's Office has reportedly deemed to have questionable credibility.

Mill, whose legal name is Robert Williams, filed a petition under the Post-Conviction Relief Act, contending that recent reports raising credibility concerns about Philadelphia Police Officer Reginald Graham warrant the withdrawal of the drug- and gun-related charges he was convicted for in 2008.

“His conviction resulted from the unavailability at the time of trial of exculpatory evidence that has subsequently become available and would have changed the outcome of the trial if it had been introduced,” the petition, filed by Brian McMonagle of McMonagle, Perri, McHugh & Mischak and Ardmore attorney Peter Goldberger, said.

Williams is currently in jail, serving a two-to-four-year sentence for violating his probation. Philadelphia Court of Common Pleas Judge Genece Brinkley handed down that lengthy jail sentence in November, stunning both Williams' fan-base and criminal justice attorneys alike, since neither Williams' probation officer nor the prosecutor on the case had sought jail time.

The case has been ensnared in controversy ever since, with members of Williams' defense team claiming, among other things, that the FBI had investigated Brinkley's handling of the case and that she had improperly pushed the rap star to switch to a Philadelphia-based manager.

So far, much of the defense tactic has focused on seeking Brinkley's recusal and questioning the judge's conduct, including arguing that she was enamored with Williams. The PCRA petition, however, focuses on the credibility of Graham, who was the only witness who testified at Williams' 2008 nonjury trial.

A recent report by The Philadelphia Inquirer said that the District Attorney's Office has included Graham on a list of police officers who the office has determined should not be put on the stand to testify during criminal trials.

The petition also says that two former police officers, Jerold Gibson and Jeffrey Walker, provided Williams' defense team with sworn affidavits refuting Graham's testimony about Williams' 2007 arrest. The officers had both been part of Graham's unit at the time Williams was arrested. Walker's affidavit, which was provided on Feb. 7, also said Graham admitted to Walker in 2007 or 2008 that he had beaten Williams during the arrest, the petition said.

Walker, however, is not without his own history when it comes to alleged misconduct. In 2014, he pleaded guilty to federal corruption charges, and was sentenced to more than three years in prison.

The petition also requests that the court order more discovery regarding Graham and the District Attorney's Office's reported list, asking that the court direct the prosecutor's office to make the list public.

A spokesman for the DA's Office declined to comment.