Betrayal at Attica, a documentary exploring one of the most famous prison riots in U.S. history, will air on HBO Max later this year.

The streaming service picked up U.S. distribution rights for the hour-long documentary, which will air later this year ahead of the 1971 Attica prison riot’s 50th anniversary in September. The Attica prison riot lasted four days, beginning Sept. 9, 1971, after prisoners took control of the Attica Correctional Facility near Buffalo, New York.

Global distribution rights to the film were picked up by Rocket Rights, a U.K. distributor that launched earlier this year via Matthew and David Frank. Its sister company, Booster, will manage VoD exploitation.

The documentary claims to tell the true story of the prison riot, in which 43 people died. The story is told from the perspective of radical lawyer Elizabeth Fink, an attorney for Attica Brothers Legal Defense. The documentary reveals alleged evidence of pre-meditated murder that has been covered up for 50 years by the State of New York.

The film also includes testimony from prisoners caught up in the riot who were subject to beatings in the event’s aftermath.