Authorities said an inmate at the Minnesota state prison in Oak Park Heights was strangled to death in his cell.
Prison staff found Shane Lawrence Cooper, 30, dead Monday afternoon, with a "ligature" around his neck.
The Minnesota Bureau of Criminal Apprehension is assisting the state's Department of Corrections and local police with the investigation.
BCA spokesperson Jill Oliveira said surveillance video helped investigators identify a suspect.
The BCA identified the suspect as Benjamin Heath Beck, 39. Beck was convicted of burglary and armed robbery in 2007.
"The individual who was questioned in this case, and is the only suspect in this case, was seen entering the victim's cell just prior to his discovery," Oliveira said.
Cooper was convicted of criminal sexual conduct last year in Duluth for the assault of a preteen girl.