WARREN – The investigation surrounding an attack on an inmate last month has concluded, and the undisclosed findings have been referred to the district attorney, Maine State Prison Warden Jeffrey Merrill said Thursday.

The 26-year-old suspect inmate has been charged with assault, Merrill said.

His identity will not be made public unless he is indicted, the warden said, citing confidentiality statutes that he says prohibit him from releasing inmates’ names.

On March 23, the suspect allegedly assaulted a fellow inmate outside the medium-security unit building. Guards, who were a distance away, witnessed the attack and responded. The 48-year-old victim, however, suffered serious bruising to the head and face. He apparently struck his head on the concrete when he fell, causing significant bleeding.

The injured inmate was taken to Penobscot Bay Medical Center in Rockport, where he remained for several days. A portion of his hospital stay was for reasons unrelated to the assault, the warden said. Upon returning to the prison, the victim also spent time in the prison’s hospital, Merrill said.

The suspect was placed in segregation for a period of time, but on Thursday, the warden would not confirm if he had been returned to his usual cell.

Both the victim and the suspect are serving lengthy prison sentences for murder. The injured prisoner has a 35-year sentence and the attacker has a 30-year sentence. Both are housed in the medium-security unit.