Tony Peralta called 911 earlier this month and confessed to killing his landlord William Blodgett 15 years ago in New Mexico.
He told police he was overwhelmed by guilt and led them to where he buried the body under the floorboards of a detached room.
He pleaded not guilty to first-degree murder on Tuesday.
Blodgett had been reported missing in 2009 and Peralta was a suspect but the case went cold until his confession.