The last Western prisoner held in an Afghan prison was flying home to Australia on Monday after seven years in a high-security facility he shared with al Qaeda and Taliban inmates.

Robert Langdon, a 44-year-old Australian security contractor, was initially sentenced to death for shooting an Afghan colleague, setting fire to his body and fleeing to the airport, where he was arrested. Mr. Langdon, who was working for the U.S. military, claimed he was wrongly convicted and didn’t get to present a proper defense during three...