Abu-Jamal, 53, once a radio reporter, has attracted a legion of artists and activists to his cause in a quarter-century on death row, and hundreds protested outside the courthouse.
Their chants could sometimes be heard inside, where a 3rd U.S. Circuit Court of Appeals panel explored defense claims of racial bias and flawed jury instructions.
"If there's one thread that runs through this case, it's racism," Abu-Jamal's lawyer, Robert R. Bryan, said afterward.
A federal judge overturned Abu-Jamal's death sentence in 2001 but upheld his conviction. Both sides are appealing that order. Prosecutors want the sentence reinstated while Abu-Jamal is fighting for a new trial.
The appeals panel is weighing three issues: whether the trial judge was racially biased, whether the judge erred in instructing jurors on the death penalty, and whether the prosecution improperly eliminated black jurors.
Bryan charged that prosecutors at the time fostered "a culture of discrimination" against blacks that the Philadelphia district attorney's office still tries to conceal.
Ten whites and two blacks served on the jury that convicted Abu-Jamal. Prosecutors struck 10 blacks and five whites from the pool, while accepting four blacks and 20 whites, Bryan said.
But the judges suggested they needed to know the racial makeup of the approximately 150-person jury pool before they could determine whether the selection had been biased.
No such record exists. "We're a day late and a dollar short with that issue, unfortunately," Bryan said.
Prosecutor Hugh J. Burns Jr. argued that Abu-Jamal did not raise some of the appellate issues at the 1995 hearing, making it difficult for him to defend the challenges now.
The jury convicted Abu-Jamal of killing Officer Daniel Faulkner, 25, after the patrolman pulled over Abu-Jamal's brother, William Cook, in an overnight traffic stop. Prosecutors call the evidence against Abu-Jamal overwhelming. Most important, Abu-Jamal was shot - by Faulkner, prosecutors say - and still at the scene when police arrived.
Abu-Jamal was not entitled to be in court Thursday, but many other key participants attended: Faulkner's widow, Maureen; his beat partner, Garry Bell; lead trial prosecutor Joseph J. McGill; and Abu-Jamal's eldest brother, Keith Cook.
"I was encouraged by their interest in the questions," Cook, 64, said of the judges. "One thing we've always done as a family is maintain hope."
A financial planner, Keith Cook was overseas in the military when Faulkner was killed in December 1981.
William Cook has uttered only a single line publicly about the shooting. "I ain't got nothing to do with it," he said at the scene.
Faulkner's widow said after the hearing that she believed any jury would have convicted Mumia Abu-Jamal.
"No matter who was on the jury, I think they would have come to the same conclusion ... that Jamal was guilty of first-degree murder," said Maureen Faulkner, 50.
About 500 pro-Abu-Jamal protesters demonstrated at the courthouse, including several from France, where one Paris suburb has named a street after him.
Marcus Shell, 35, of Philadelphia, said Abu-Jamal did not get a fair trial because of his identity as "a former Black Panther, the voice of the voiceless."
"Mumia represents a lot of blacks locked up in prison today," Shell said. It's uncertain when the court might rule, but decisions typically are issued within several months.