A man held in a Seward maximum-security prison for a fatal Anchorage stabbing 15 years ago died Monday evening in an apparent suicide, according to state corrections officials.

Antonio Roberson, 38, died shortly before 10 p.m. Monday at the Providence Seward Medical Center, the state Department of Corrections announced Tuesday.

“Roberson was discovered unresponsive in his cell at the Spring Creek Correctional Center by an on-duty correctional officer during a routine security check at approximately 8:50 p.m.,” DOC officials wrote in a statement. “Life-saving measures were attempted immediately, and Roberson was transported to the hospital, where he was pronounced dead.”

Megan Edge, a DOC spokeswoman, said a preliminary investigation indicated that Roberson took his own life. It wasn’t immediately clear what means were used, or how much time had passed between the prison’s previous security check on Roberson’s cell and the one that found him unresponsive.

Roberson had been charged with killing Ronald D. Stevens, who was stabbed outside the Burger Stop restaurant on Benson Road in March 2002. Court records show that Roberson pleaded guilty to second-degree murder in the case.

An Alaska Court of Appeals ruling, denying an appeal by Roberson of his 60-year sentence, said Roberson told police that Stevens had offered him a ride in his car, then forced him to perform sexual acts at various stops in town. When they stopped at a store in Eagle River, Roberson bought a hunting knife he later used to threaten then stab Stevens.

Roberson had been in DOC custody since 2002, Edge said. He would have become eligible for parole in 2022, and could have been released as early as 2048. His death is the department’s fourth in custody this year.