An inmate was found strangled in his cell at Minnesota’s prison in Oak Park Heights Monday — the first killing inside the maximum-security facility since it opened in 1982.

Corrections officers identified a suspect immediately, after finding the photo badge of a second inmate, which apparently fell onto the victim’s body during the struggle.

The victim, Shane Cooper, was strangled by a shoelace tightened around his neck with a pencil used as leverage, sources said.

Cooper, 30, of Superior, Wis., had been convicted of criminal sexual conduct with a child and placed in the prison last year.

The suspect has been identified as Benjamin Heath Beck, 39, of Fillmore County. In addition to the ID badge found on Cooper’s body, video surveillance captured Beck entering Cooper’s cell shortly before the body was found, according to the Minnesota Bureau of Criminal Apprehension (BCA).

Cooper’s body was found by corrections officers who came to his cell about 4:50 p.m., during the evening’s first prison count, when the prison’s electronic monitoring system indicated that his cell was not locked.

Beck, who is serving a prison term for aggravated robbery, has been interviewed by agents from the BCA, which is assisting the Department of Corrections’ Office of Special Investigations. He is being held in a prison segregation unit; murder charges are expected to be filed by the Washington County attorney’s office early next week.

Cooper and Beck were known to socialize together and were viewed as friends, sources said. However, they said, Beck may have recently learned that Cooper was a convicted child molester. It is common in prisons for child molesters to be targeted by other inmates who view the crime as particularly abhorrent.

Prison officials and medical staff were examining a second inmate death that took place about the same time as Cooper’s killing, but no foul play is suspected, sources said.