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PHILADELPHIA (CBS) – A deposition will take place on Monday in the case of Mumia Abu-Jamal, who is seeking a new trial in the death of a Philadelphia police officer.

Abu-Jamal was convicted in the 1981 murder of Philadelphia Police Officer Daniel Faulkner.

His defense team says they need a document to prove their case for a retrial, but the document cannot be found.

A judge agreed to depose the employee who wrote the document.

His lawyers say Abu-Jamal’s rights were violated during appeals because of bias by then-state Supreme Court Justice Ron Castille a former Philadelphia district attorney.