Mineral, Washington murders

In August 1985, Stephen Harkins, 27, and his girlfriend Ruth Cooper, 42, left their Tacoma home for a weekend camping trip at Tule Lake in Pierce County, Washington. When they failed to return to work the following Monday, their families reported them missing. On August 14, hikers discovered Harkins' body near a remote campsite; he had been shot in the head while apparently asleep in his sleeping bag. The couple's pet dog was also found shot to death nearby. Investigators at the time considered a possible connection to the earlier murders of a couple from Kent, Washington, in March 1985. On October 26, 1985, a skull later identified through dental records as Cooper's was found near Harts Lake, about 1.5 miles from where Harkins had been discovered. Two days later, her body and purse were recovered nearby. A tube sock had been tied around her neck, and while an autopsy cited "homicidal violence," a spokesman later said she died of a gunshot wound to the abdomen.

Just over a month later, on December 12, 1985, Mike Riemer, 36, his girlfriend Diana Robertson, 20, and their two-year-old daughter Crystal traveled from Tacoma into Pierce County, reportedly to find a Christmas tree and for Riemer, an animal trapper, to check his traps. That evening, Crystal was found alone outside a Kmart store in Spanaway, about 30 miles away, and was eventually placed with her grandmother after being in temporary foster care. She was reportedly unable to provide useful information about what happened to her parents. Extensive searches failed to locate Riemer's truck or the missing adults until February 18, 1986, when Robertson's body was found half-buried in snow near a logging road off Washington State Route 7, south of Elbe. Riemer's truck was found nearby, containing a note reading "I love you, Diana," which Robertson's mother identified as Riemer's handwriting, along with bloodstains on the seat. An autopsy found Robertson had been stabbed seventeen times and, like Cooper, was found with a tube sock tied around her neck.

Riemer's disappearance led investigators to initially suspect he may have killed Robertson before fleeing, though no clear motive was established; an alternative theory held that Riemer was himself a victim of the same perpetrator responsible for the other deaths. Contemporaneous reporting noted that Riemer had been charged with domestic assault against Robertson in October 1985, though the couple had reconciled by the time of their disappearance.

The case remained unresolved for over two decades until March 18, 2009, when hikers found a partial human skull within a mile of where Robertson's body had been recovered in 1986; it was later determined to belong to Riemer. Investigators said Riemer could have been a homicide victim, though his cause of death could not be determined, and a gunshot wound to the head was ruled out based on the skull's condition. The case was featured on the television series Unsolved Mysteries in September 1989 and remains unsolved.