Live from death row: as Mumia Abu-Jamal's case reaches a new turning point, prison activists reflect on his significance to the reform and abolition movements.(FEATURE)

HALF A LIFETIME AGO, Mumia Abu-Jamal was sentenced to death for killing a rookie cop on the streets of Philadelphia. In the decades since, the former radio and print journalist has authored five books and written and recorded hundreds of articles and speeches criticizing his captors and the government that imprisons more than two million of its people. Despite the constraints of 23-hour lockdown and Plexiglas sound barriers, he became a preeminent "voice of the voiceless," framing the modern prison abolition movement.

Abu-Jamal's commentaries, a rich baritone echoing off the walls of a maximum-security visiting room, air regularly on 185 radio stations around the ...