Seven inmates have been charged in a 2015 riot at a private prison in Oklahoma in which four prisoners were stabbed to death.

Online court records indicate the charges were filed Monday in Payne County District Court. Each defendant is charged with participating in a riot, a felony punishable by up to life in prison.

The deadly melee occurred on Sept. 12, 2015, at the Cimarron Correctional Facility in Cushing, which is a private prison owned and operated by Tennessee-based Corrections Corporation of America.

Authorities said at the time that the riot started when a dispute between two rival prison gangs became violent.

Payne County District Attorney Laura Thomas didn't immediately return telephone and email requests for comment.