The Middlesex District Attorney’s office said 48-year-old Shawn Marsh entered the plea and was sentenced Thursday to 15 to 18 years in prison.
Marsh was charged with murder two years ago in connection with the shooting of 29-year-old Rodney Wyman of Simsbury, Conn.
Prosecutors said Wyman was shot at a Malden motel on Aug. 22, 1983, when Marsh and another unidentified person broke into his room intending to rob him. An autopsy found Wyman died of a single gunshot wound that punctured his heart, aorta and a kidney.
Updated technology allowed police to take another look at fingerprints from the scene, leading them to Marsh. He was arrested in Holyoke in September 2011.