Officials are continuing to investigate a prison assault on an inmate who remained in critical condition Friday night in University Hospital.

Raymond Joseph Malin, 25, serving time for the throat-slashing death of a 14-year-old girl, underwent surgery for head injuries Thursday after he was found injured in his cell block in the prison's maximum-security section. Malin and other prisoners had been out of their cells on recreation time just before he was discovered.Prison officials have begun an extensive investigation into the assault and have identified at least one suspect, said David Franchina, director of the division of institutional operations at the prison.

"We've gathered physical evidence and an enormous amount of testimony," he said, but added that most of the testimony has not been very helpful.

"Unfortunately, it's common in an institution when something like this happens everyone seems to have had their backs turned at the time," he said. "It's very difficult to prosecute a case in prison."

Franchina said that when enough evidence is collected the Salt Lake County attorney's office will be approached for prosecution.

Malin pleaded guilty in March to the death in 1987 of Jana Dawn Hoercherl, whose body was found behind a telephone switching building in Kearns.