Mineral, WA. Murders

I picked this case first to post because of the proximity of Ft. Lewis where I was stationed at the end of the 1990’s. I’ve visited Mt. Rainier more than a few times during this period.

The case of Mike Riemer and Diana Robertson is one of the eeriest and most puzzling unsolved mysteries of the 1980s, blending elements of true crime, the wilderness, and an ominous message left behind. This is a detailed account of their deaths and the chilling circumstances surrounding their case.

 

On December 12, 1985, 36 year old Mike Riemer  and 21 year old Diana Robertson along with their two-year-old daughter, Crystal, set out on a trip into the forests of Washington State. Their destination was the remote backwoods of Pierce County, near the foothills of Mount Rainier. Mike, a roofer by trade, was also a trapper and outdoorsman who frequently set traps for animals in the area. Diana, his girlfriend, accompanied him that day, presumably to check traps, as they had done before.

Also with them was their young daughter, Crystal Louise, a bright-eyed toddler who was about to be at the center of a chilling mystery.

 

Later that same day, an unsettling discovery was made: Crystal was found wandering alone inside a Kmart in Spanaway, Washington, about 30 miles away from the wilderness area where her parents had gone. The toddler was seemingly unharmed, but she was unable to explain what had happened to her parents. Being only two years old, she couldn’t provide any clear answers—only vague statements about "Mommy being in the trees."

The police were immediately concerned. Where were Mike and Diana? Who had left Crystal in the store, and why?

 

Fast forward, two months later, on February 18, 1986, a hiker stumbled upon Diana Robertson’s body near a logging road in Mineral, Washington. Her body was partially covered by a blanket, and nearby, police found a blood-stained tube of lipstick and a manila envelope with the word "Sorry" written on it in red ink.

Diana had been brutally stabbed 17 times, and authorities noted that her cause of death was "homicidal violence." Next to her body, there was also a stack of neatly placed sticks, a seemingly deliberate act. Mike Riemer, however, was nowhere to be found. His truck, a red 1982 Plymouth pickup, was discovered about a mile from the crime scene, further deepening the mystery.

With Diana’s murder confirmed and Mike missing, investigators started to suspect that he had killed Diana and abandoned Crystal before fleeing. There was some troubling background information that led police to consider Mike as a suspect: he and Diana had a history of domestic violence, and friends said their relationship was volatile. Some believed Mike may have snapped, killed Diana, left their daughter in a safe public space, and then vanished—either escaping or committing suicide in the woods.

However, there was no concrete evidence to support this, and no sign of Mike's body. If he had fled or died in the wilderness, why wasn’t there any trace of him?

YEARS passed with no sign of Mike, and people began speculating whether he was truly the killer—or possibly another victim.

In a chilling turn, Diana’s murder was linked to another unsolved double homicide from 1985. Earlier that same year, another couple, Steven Harkins and Ruth Cooper, had been found murdered in the same general area of Pierce County.

Harkins’ body was discovered in August 1985 at a campsite with a gunshot wound to the head.

Cooper’s body was found two months later, in October, just 1.5 miles away. Like Diana Robertson, she had been stabbed in the chest.

The condition of Cooper’s body was eerily similar to Diana’s—she was partially covered and found without shoes.

This meant that whoever had killed Harkins and Cooper might also have been responsible for Diana’s murder. If that was true, then was Mike also a victim rather than a murderer?

 For years, the case remained open, with theories circulating that Mike was either a killer on the run or a missing murder victim himself.

Then, in March 2011, a hiker in Lewis County, Washington, made a shocking find: a human skull in the woods. Dental records soon confirmed that the remains belonged to Mike Riemer.

The discovery threw the original murder theory into question. Mike's remains were found about a mile from where Diana had been discovered, suggesting that he had likely died in 1985—around the same time as Diana. However, the cause of death could not be determined, and only his skull was found. This left open several possibilities:

Mike had been murdered alongside Diana by an unknown killer.

Mike had killed Diana and then taken his own life in the woods.

Mike had been attacked after fleeing the scene, possibly by animals or another unknown person.

With so little evidence, authorities were unable to say definitively whether Mike was a murderer or another victim. However, many now lean toward the theory that a serial killer was responsible for the deaths of both couples.

 Who left Crystal at the Kmart? Was it Mike before he died, or was it someone else?

What did the word "Sorry" on the envelope mean? Was it a confession from Mike, or something left by the true killer?

If Mike was innocent, why did he vanish without a trace for decades?

Could the killer have been someone entirely unknown, lurking in the Washington wilderness, preying on couples?

To this day, the case remains unsolved. While some still believe that Mike Riemer was the killer, the discovery of his skull suggests otherwise. If he was a victim, then his and Diana’s killer has never been caught.

 

MY FINAL THOUGHTS:

The mystery of Mike Riemer and Diana Robertson is one of the Pacific Northwest’s most unsettling unsolved cases. It has elements of a horror story—a missing couple, a child left behind, and cryptic clues like the word "Sorry" scrawled on an envelope.

Was this the work of an unknown serial killer hunting in the Washington woods? Or did Mike have a tragic breakdown, killing Diana before succumbing to the elements?

The truth may never be fully known. What happened in the forests of Pierce County in 1985 still haunts those who remember the case. Admittedly, I did not know much about this case when I first started typing this up.  As of 2020, investigators were working to extract a DNA profile from Mike Riemer's remains to compare with DNA found on the ligature used to bind Diana Robertson's hands. They also planned to compare this profile to any DNA evidence from the earlier murders of Steven Harkins and Ruth Cooper. HOWEVER, the results of these DNA tests have not been publicly disclosed, leaving the case STILL unresolved.

 Something tells me that either the DNA was so degraded that it couldn’t be used… or it wasn’t a match. An update would have been nice either way. I hate the fact that it seems resources were pushed back for nearly a decade, but I understand. Newer cases pop up with a higher probability of being solved rather than trying to solve a murder from the 80’s. What are your thoughts?