A man has pleaded guilty to killing a fellow inmate during a right at a northwestern Pennsylvania state prison last year.

Twenty-six-year-old Trevon Coleman pleaded guilty to third-degree murder before an Erie County judge on Thursday.

State police say Coleman slammed 33-year-old Job Knighton to the ground and stomped his head after first punching Knighton and stabbing him with a pen in the cheek. That happened at the State Correctional Institution-Albion in February 2015, and Knighton died at a hospital five days later.

Prosecutors and defense attorney Bruce Sandmeyer say they're waiting for results of a mental evaluation to determine whether Coleman will be placed in a state prison facility for mentally ill inmates.

Coleman faces up to 40 years in prison when he's sentenced June 2.