VANCOUVER, Wash. (AP) — A suspected serial killer accused in the slaying of 17-year-old Martha Morrison in 1974 has pleaded not guilty. The Columbian reports Warren Forrest was arraigned Friday in Clark County Superior Court on one count of first-degree murder in the Portland, Oregon, girl’s death. Her remains were discovered in October 1974 by a hunter but they were not identified until July 2015. Forrest is believed to be responsible for the abduction and slaying of six women and girls in Clark County in the 1970s. Forrest is service a life sentence for the murder of 20-year-old Krista Blake, 20, who was last seen July 11, 1974, climbing into his van.