PHILADELPHIA — Former death-row inmate Mumia Abu-Jamal asked a judge Monday to vacate his previous failed appeals attempts so he can again appeal his case.

A judge continued the hearing until Aug. 30 after a document Abu-Jamal's defense said they need to prove their petition was not found. The judge also approved a deposition of the employee who wrote the document to see if she can remember the contents.

Abu-Jamal's lawyers are petitioning under the Post-Conviction Relief Act, arguing that the 64-year-old's rights were violated during previous appeals because of what they say is the bias of state Supreme Court Justice Ronald Castille.

Castille is a former Philadelphia district attorney. As prosecutor, his office succeeded in getting the State Supreme Court to uphold Abu-Jamal's conviction.

Abu-Jamal's attorneys say Castille should not have had any involvement in deciding his appeals after he became a judge.

Philadelphia District Attorney's office spokesman Ben Waxman said the office looked for any documents that would be relevant to the argument that Castille had direct personal involvement in the case when he was prosecutor, but found none.

The judge also asked the district attorney's office to reach out to Castille to see if he has the document in question in his personal papers.

Abu-Jamal, a former Black Panther, spent 29 years on death row following his conviction in the 1981 murder of white Philadelphia police Officer Daniel Faulkner. Abu-Jamal's sentence was reduced to life without parole in 2011.

Abu-Jamal has maintained his innocence and has become a symbol for groups seeking criminal justice reform.