Officials are investigating the Sunday death of a prisoner at the Central Utah Correctional Facility in Gunnison.

Steven Davis, 66, was found “unresponsive” in his cell at the Gunnison prison, according to a news release from the Utah Department of Corrections. He was declared dead a short time later.

How he died has not been determined, according to officials, who did not say if foul play is suspected. The prison — which houses about 1,760 inmates — was placed on lockdown Sunday as an investigation into the prisoner’s death began.

Davis had been in prison since December 1983 after he was convicted of first degree sodomy of a child and parole violations, records show.

He was the second inmate to die at the Gunnison prison this month. On Sept. 2, a prisoner was pronounced dead after his cellmate reported that he was not moving.

Last month, a fight at the prison involving 15 prisoners on Aug. 21 sent five people to a hospital and prompted a lockdown at both the Gunnison facility, as well as the state prison in Salt Lake City.