Campbell was last seen in Anaheim, California on April 16, 1982. Police investigating his disappearance learned that he met his best friend, Lawrence Rayburn "Larry" Cowell, and another man, Donald Dimascio, on the day of his disappearance. The three men were supposed to fly to Fargo, North Dakota, but instead the plane flew west out over the Pacific. Sometime during the flight, investigators believe, Campbell was murdered, possibly during a drug-related robbery. They theorized that Cowell piloted the plane and had Dimascio strangle Campbell, and the two men threw his body into the ocean near Catalina Island.

Cowell was arrested after authorities discovered he had Campbell's Pantera sports car and was stripping it and selling the parts. He had several prior convictions and, at the time of Campbell's disappearance, was out on bond awaiting trial for vehicular manslaughter; he had killed someone in a drunk driving accident in 1980. He was later convicted of that charge and sentenced to 180 days in jail.

Cowell admitted Campbell's death, but stated it wasn't premeditated and Dimascio acted in self-defense after Campbell threatened him with a gun. Both men were convicted of murder, robbery and conspiracy to commit murder. An appeals court later overturned Cowell's conviction, but he was convicted again at his second trial. Dimascio was sentenced to life in prison without parole. He died in prison. Cowell is serving two terms of twenty-five years to life in prison. He applied for parole in 2011 and was denied. Campbell's remains have never been located.