According to this article, remains found three weeks ago near Mineral, Washington have been identified as Michael Lloyd Riemer, who disappeared from Pierce County, Washington in 1985. He was 36 years old.
The case is an odd one. Michael disappeared with his girlfriend, Diana Robertson, and their two-year-old daughter, Crystal Robertson. They had gone on a combination trapline check and Christmas tree hunt in the woods. That afternoon, Crystal turned up wandering around a
Wal-Mart K-Mart, alone. She said “Mommy is in the trees.” In February 1986 (two months after she went missing), Diana’s body was found on an old logging road. She’d been stabbed 17 times and strangled with a sock. Michael’s truck was nearby, bloodstained, with a note saying “I love you, Diana.” There was no indication of his whereabouts and the police weren’t sure whether he was a murderer or a victim, though it’s worth noting that the couple had a history of domestic violence.
Michael’s skull was also found on a logging road, about a mile from where Diana was found 25 years ago. This article says they can’t determine the cause of death; apparently all that they found was the skull. No word on how long they think it’s been there.
I think it’s likely that the case will remain an unsolved mystery.