Sheriff's spokeswoman Stacy Brown said the remains were positively identified as Michael Lloyd Riemer, who was reported missing in December of 1985, along with his significant other, Diana Robertson.
The couple's 2-year-old daughter, Crystal Robertson, was found wandering alone at a K-Mart store in Spanaway the day the two were last seen. Detectives didn't know who the girl was until her family saw her pictures in the news and came forward. At that point, all the girl could say was that "Mommy was in the trees."
The girl's words set in motion a massive search. The body of Robertson, who was 21 when she disappeared, was found in February 1986 on an abandoned logging road north of Mineral, Wash. She had been stabbed multiple times.
Brown said several searches were conducted in 1986 to find Riemer, and the case was featured on an episode of "Unsolved Mysteries" in 1989.
Investigators followed up numerous tips, but Riemer's body was not found until March 30 of this year when a hiker discovered the skull. The remains were located about one mile from where Robertson was found dead.
Riemer was considered a person of interest in Robertson's death at the time of her disappearance, Brown said, as well as in the murder two campers a few months prior. The remains of Stephen Harkins and Ruth Cooper were found close by.
But detectives say there's also the possibility that Riemer, too, is a victim. His cause of death has not been determined.
"Unfortunately, finding this is not leading us any closer to what actually happened that day. Really, all it tells us is that he is not out, running around," said Brown.
The couple's daughter grew up in the care of relatives, and is now 27 years old.
"I think the whole case has obviously been tough for her. It was her mother and her father," said Brown.
Detectives are still trying to determine exactly what led up to the two deaths, and asked anyone with information to call the Lewis County Sheriff's Office at (360) 748-9286 or Crime Stoppers 1-800-748-6422.