The Correctional Service of Canada says 65-year-old Gordon Pawliw died of apparent natural causes at Abbotsford Regional Hospital on Nov. 10.
Pawliw, Rodney Camphaug and Roderick Schnob were sentenced on April 26, 1985 for the shooting of Dianna Van Dooren at her Duncan, B.C., home, a year earlier.
A three-month trial heard the Crown believed the trio had gone to Van Dooren's country home to kill her husband, Dennis, over a drug deal but the plan collapsed and the 57-year-old woman was shot instead.
In an unrelated incident, Dennis Van Dooren was shot to death in an altercation with another man in the Cowichan Valley in 2009.
Corrections officials say that as in all cases where an individual dies in custody, police and the coroner have been notified of Pawliw's death and the Correctional Service will also review the incident.