A serial killer is suspected in the murder of a young mother.

Mike Riemer & Diana Robertson

Diana was found murdered


A tube sock was tied around her neck

On the morning of December 12, 1985, Mike Riemer, his girlfriend Diana and their daughter, Crystal, set out for a day in the mountains near Tacoma, Washington.  Diana had just turned 21 and had known her 36-year-old boyfriend since she was 17.  The couple drove up into the forest south of Tacoma, a scenic region often frequented by campers and nature lovers.  They planned on finding a Christmas tree, and as Mike was a trapper, he intended to check his animal traps.

Later that same afternoon, Crystal was found at a department store near Tacoma.  She seemed stunned, silent, and her parents were nowhere to be found.  After being checked at a local hospital, Crystal was sent to a temporary foster home.  Three days later, after being recognized from a news broadcast, Crystal was identified by Diana’s mother, Louise Conrad:

There was a message: “I Love You, Diana”

“And as soon as she saw me, she put her arms out and said, ‘Gramma.’  And they put her down and she ran to me and, and I’ve had her ever since.”

Crystal’s parents had vanished without a trace.  When Crystal was asked where her parents were, all she could say was “Mommy is in the trees.”  Four months earlier, the forest area where her parents disappeared had been the scene of two brutal murders.  Initially, police made no connection between the couple’s disappearance and these murders.  But soon a connection would prove inescapable.  A massive search was launched the same weekend the couple disappeared.  Mike’s best friend, Steve Tew, scoured the countryside on the ground and from the air:

“We searched from the spot where Mike would normally start his trap plans and we followed the whole, trap plan.  And we searched for probably two or three hours… nothing.”

Police found blood stains on the car seat

Then, two months after the couple disappeared, a man walking his dog deep in a forest near Elbe, Washington, discovered the body of Diana Robertson.  Crystal was correct when she said that her mother was “in the trees.”  Diana Robertson was lying dead in the forest alongside Mike’s truck.  She had been stabbed 17 times and a tube sock was tied around her neck.  There was no sign of Riemer.  When Detective David Neiser of the Lewis County Sheriff’s Department searched Mike’s truck, he found bloodstains on the front seat:

“Unfortunately, after two months and about two weeks, some of the characteristics of the blood were lost.  And they were not able to tell us what the blood type was.  But they were able to tell us the blood was human.”

Police then found another baffling clue.  Displayed prominently in the truck’s cab was an envelope that read, “I love you, Diana.”  Diana’s mother Louise believed the handwriting was Mike’s:

“I have cards that he had given to her on different holidays and things… he signed exactly the same way.”

Ruth Cooper had been found four months earlier

But according to Detective Neiser, the FBI’s analysis of the handwriting came back inconclusive:

“Why did someone put that there?  Was it Michael Riemer as a final,’goodbye Diana, I’m sorry?’  Or was it someone who put it there to throw off the authorities and make them think that.”

Police believed that this killing was possibly connected to a double murder that had occurred four months earlier, just 15 miles from where Diana Robertson was discovered.  These murders occurred in Pierce County, an area where Mike Riemer was known to set his animal traps.  A man named Stephen Harkins was found dead in his sleeping bag, shot in the forehead.  His companion, Ruth Cooper, was discovered two months later.  She too had been shot to death.  And like Diana, a tube sock had been tied around her neck.  According to Detective Neiser, the tube sock on Diana had been tied with exactly the same type of knot as in the earlier murder:

“At a later date, I asked to observe the sock, which was used around the neck of Ruth Cooper. And when he dumped it out on a desk in the evidence lab, the evidence technician let out a little whistle, because knowing nothing about the case, he could see that it was the same as the one I had brought with me from Diana Robertson.”

Police considered two theories.  One was that an unknown serial killer had murdered both couples, and then hid Riemer’s body.  The second theory was that Mike Riemer was the serial killer. Mike Riemer had a history of domestic violence.  According to Diana’s sister, Darlene Robertson, Riemer frequently beat Diana:

“He beat her up.  He took everything out on her.  He blamed her for things that he did.  If he was seeing somebody else, he would turn it around like Diana was seeing somebody else and justify it in his own mind.”

Police now had enough circumstantial evidence to issue a warrant for Riemer’s arrest.  But according to Detective Neiser, there was one glaring problem:

“We can’t prove he’s alive and we can’t prove he’s dead.  If we could show that he was dead, then it would be my belief that there’s an unidentified third party who’s going around killing people out there.  However, if we can prove that he’s alive, he immediately becomes a suspect and that changes the situation dramatically.”


The skull of Mike Riemer was discovered recently by a hiker about one mile from where Diana Robertson’s body had been found 25 years earlier.  No other traces of Riemer have been found, and his cause of death could not be determined.

Watch this case now on Amazon Prime in season six with Dennis Farina. Also available on YouTube with Dennis Farina. Various seasons available now on Hulu.




  1. Crystal

    it saddens me to see such silliness made in comments about my families tragedy. if I’m not pointing a finger or placing blame what right does anyone else have?


    • Jennifer Stephens

      I’m sorry for the loss of your parents! I hope that you and your gramma had a wonderful life, and hope this crap has not followed your family causing grief. I’m 36 so about your age, I live in Missoula, MT.


  2. Snodgrass

    Keep in mind that the Robertson murder probably happened during broad daylight. The daughter was found at the Kmart in the afternoon and it gets dark early in the Washington forest in December. If Mike were the one to commit Diana’s murder then he would be returning back to the site of her death near Mineral in total darkness, where he was to commit suicide. Does this make any sense? If you were going to kill your spouse and then commit suicide would you bring your 2 year old daughter with you for the ride? Would you then return to Spanaway which is almost an hours drive from Mineral or Elbe, drop off your daughter outside a department store, and then drive back to the woods to commit suicide? I understand that someone’s state of mind can make them do crazy things; however, I just don’t believe that Mike Riemer did all of this. I have two daughters and I would never leave them alone like that to fend for themselves. Wouldn’t you drop the kid off at a friends house or if you are going to abandon the child why not just leave her at home for a relative or neighbor to find.


  3. Leigh

    It’s compelling that no other victims strangled with a tube sock in that unique way were ever found, following this murder. But, if we believe that Mike killed Diana, then drove his daughter to safety before coming back to kill himself; then, we must concede that he was also the killer of Stephen Harkins and Ruth Cooper. It sounds as if he had the rage to be a killer. I would be surprised though, it he was able to kill his girlfriend in such a brutal and personal way, and then cool down enough to take his kid to a department store. He would have been covered with blood, unless he just tied Diana up, took his daughter to town, and then returned to finish killing his girlfriend. He may not have been the killer at all; maybe, the killer got some sick kick by ‘sparing’ the child. Creepy story, will most likely never be solved. I can imagine that poor child had a difficult time healing from this terrible trauma.


  4. Sheepdipped

    It could have still been a murder/suicide. Doubtful, but it’s almost even more doubtful that a serial killer would kill the couple, then drive the young daughter to the store and drop her off. It’s just strange all around. If mike was the killer he would have to kill diana, drive the daughter to the grocery store parking lot, then drive back to the crime scene, walk deep into the woods and kill himself. It’s unlikely but still a possibility. There was blood (probably from Diana) in the truck. And I could see his motivation for not wanting to hurt his daughter.


  5. tabitha

    How did the little girl get to the store? Who dropped her there? I don’t think she just walked from the woods to a store….


  6. Johnny

    It’s a real shame. Mike & Diana were a good-looking couple. I must have seen a dozen of these camp murders or disappearances. Seems like many serial killers work out of Washington terrain. The heavy foliage and mountain areas make good places to find victims in desolate areas. Mike was not the killer with the skull discovery. It would be difficult to theorize what happened here. The killer must have been familiar with the couple. Probably forced Mike to write the I Love You thing and then killed him. I don’t want to think about the torture and pain Diana was forced to suffer. This was 1985 so enhancements in DNA technology could solve the case. It’s doubtful that the killer was well-versed in extensive DNA and Criminology. Maybe, they can find something with his DNA.


  7. Chloe

    What an incompetent bunch of morons those cops are. “Enough circumstantial evidence to put out a warrant” seriously you idiots?? All because they were too incompetent to solve the case themselves.
    How embarrassing that is for this guys family, not to mention how hard the actual killer must have laughed when he learned they were putting a warrant out for the guy that HE killed!!
    It’s because of incompetent police work and idiots like these cops that it should not be allowed to arrest someone on circumstantial evidence alone. That has killed a lot of innocent people. America is one effed up country!!


    • Anonymous

      As long as people like you vote here


    • Echo

      Obviously you lack the capacity to understand what was going on. They didn’t know the guy was already dead and they said the evidence was circumstantial. Comments like these are the product of over a generation of poor parenting. Raising kids without an authoritative figure in their life and teaching them to do whatever feels good is going to be the downfall of western culture.


    • Dave

      Well let’s see, Diama is dead. The child spared. Mike’s body nowhere to be found. So no body means he could very much be alive. So of course he’d be a suspect. Putting myself as a detective working this crime. Again Diana was killed, their child spared, Mike nowhere to be found. Domestic violence. He’s the number 1 suspect.

      I don’t think he did it. I could understand why he’d kill his spouse. But why the other 2 people? But at the time it’s a no brainer to suspect Mike. I believe he was a victim of homicide and not murder/suicide.

      As for the child, perhaps the killer didn’t wanna harm a child. Plus she was far too young to be a threat in both stopping him or giving a description.