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

A young caucasian couple on a couch. Diana Robertson and Mike Riemer, Diana has long brown hair and Mike has long blonde hair.

Mike Riemer & Diana Robertson

A body is laying face down on the ground in a forest, there is a truck parked nearby.

Diana was found murdered

CASE DETAILS

A close up on the back of Diana's head, there is a tube sock gagging her and knotted behind her head.

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:

A close up on a note that reads 'I love you Diana,'

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.”

There are multiple blood stains on the seat of the car.

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.”

Three police officers stands next to the corpse, covered by a white sheet. There is crime scene tape circling the area.

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.”

Update:

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.

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29 Comments

  1. Avatar

    Bill Blaski

    Stephen Harkins was killed with a .22 did, Did Mike Reimer own a .22? Cooper also killed with a .22. Sock used to lead or pull her, women separated from the man. Diana was stabbed and lead pulled with sock. Too many similarities in these 4 murderers, why is there not a task force investigating 4 murders? I pray for the victims families and wish them peace.

    Reply

  2. Avatar

    Amanda Doherty

    I suspect next to non of you have ever studied serial killers at all? If you had you wouldnt be spurting out this much nonsense

    Reply

  3. Avatar

    Brynn

    Why hasn’t this cold case been reopened using DNA? I came from you-rube where it was a case called mommy’s in the trees. It had the same lack of facts as this article. Was the mother killed where they found her? Did they bring in cadaver dogs when they found the skull? The little girl can’t remember who brought her to Kmart? Man? Woman? Someone she knew? Seems like lots is missing here and I can’t find much useful information anywhere. I read above that the little girl now woman and a cousin said to leave it alone… that’s strange why wouldn’t you want to know what happened to your mother and her boyfriend (not sure if he’s her dad or not) if there’s a serial killer or was maybe it could save lives or give the family of the other couple closer, if they’re connected. If anyone knows of a better resource for info please share.

    Reply

  4. Avatar

    J

    Diana is my cousin you people are talking about. We are so fortunate that Crystal was spared by whoever did this horrible crime. Please respect Crystal’s wishes and stop speculating about who, what, when, and where. If you know something relevant say something otherwise keep you opinions to yourself. Our family has had enough tragedy we don’t need strangers who don’t know anything to continue to speculate about how it happened. If you have any real information let unsolved mysteries know. Otherwise just leave us alone so we can grieve and go on with our lives. Bad things happen to good people every day, please stop making it worse for our family.

    Reply

  5. Avatar

    Dean

    Another episode missing from the prime video lot…..redicolous

    Reply

  6. Avatar

    Charles

    I truly think this was the work of a serial killer; however, that also presents a lot of grey areas. Most serial killers keep murdering and I suppose it is valid to say that some never do get caught. The rituals involved, the symbols, the carnage of the murders…it all points to a serial killer.

    Reply

    • Avatar

      Ron Ferguson

      Dianna called me in the fall not sure of the year and told me she wanted to leave her boyfriend and could she come back and stay with me very regretfully I said no she said she was afraid of him

      Reply

      • Avatar

        Ashley

        Ron, would anyone in the family be interested in telling their story on a local podcast? I know in other comments it seems everyone just wants to be left alone, but if there’s any chance one of you wants to talk about the people you’ve lost and what you’d like to see happen in this case from law enforcement, I’d love to interview you. More media attention might be what leads to a crucial new tip or it could put pressure on police to bring their focus back to solving these horrible crimes.

        Reply

  7. Avatar

    thinkingoutloud

    i think mike killed diana and then wound up killing himself sometime later. he probably wrote the envelope cause he was feeling guilty about abusing her / killing her. he either dropped crystal off at the store and then went into hiding OR maybe he had a friend help him bring crystal to the store while he went into hiding.
    they only found his skull…no other body parts and the death was inconclusive. that could mean mike was killed sometime after diana was killed or he was killed and his skull was brought back there later. i don’t see how authorities could miss a dead body / skull less than one mile from where diana was found and on top of it, no other sightings of his skull or 25 years. it’s also possible after all those years he was feeling super guilty and remorseful and killed himself near the site of where he killed diana.

    and if mike did have a temper and was abusive, maybe he was a serial killer. he killed the couple years earlier and did the same to his GF and wound up killing himself years later

    Reply

  8. Avatar

    FF

    I feel like if Crystal remembered mommy was in the woods she would remember if it was daddy that dropped her off. I don’t think it was her dad. Kids remember more than they get credit for. Yes she was young but still feel like when someone asked who brought you here (meaning the store) she would have simply said daddy.

    And I am just spitballing but as far as the note goes maybe Mike wasn’t sure if Diana was dead but he was injured (hence the blood in the truck) so he left a note for her and tried to escape or get help. His partial remains found a mile from the scence. A mile might not seem like a lot but when on foot, injured and disoriented it can seem never ending .

    It only said that Diana’s body was found by the truck that doesn’t mean that’s where she killed or sustained most of her injuries.

    It’s also possible that Mike was off checking traps or gathering supplies. Diana and Crystal stayed behind and got attacked, ran off trying to escape. Mike comes back to see the blood and stab marks in the truck seat. Diana and Crystal missing, he leaves the note, goes to look for them. Diana disoriented circles back to the truck where she succumbed to her injuries and the killer hears Mike yelling and then goes off to kill him as well. Which is how he ended up about a mile away. All the time having Crystal secured in the killers own vehicle.

    We will never really know what happened. I feel really bad for Crystal having to live with all the questions and speculation. I am sorry that your family had to endure such tragedy. I just hope that with the discovery of your father’s partial remains you have felt some closure in the possibility that he didnt do the horrible things he had been accused of.

    Reply

  9. Avatar

    Tiffany

    Crystal, have you been able to read the autopsy report for your Mother and for the other couple?
    Have you been able to read the police files for yourself?
    Perhaps there are some hidden clues there. When you are too close to a situation, it is difficult to look at all of the facts objectively. I found your case on Websleuths, and I can’t help but want to help you find a potential serial killer. It is known that serial killers evolve and their MO changes slightly, but there will always be similarities.

    Did you realize that both sets of victims were 15 years apart in age and both men loved the outdoors? For both couples, 1 body was found right away, while the other took longer to find.

    I would love to research this more… but I am finding it difficult to find the public records for the autopsy’s and police records.

    Reply

    • Avatar

      Catrina

      Since all four cases are still unsolved, the autopsies are still potential evidence, closed to public view. Also, please everybody, quit telling Crystal what to do. She’s an adult, she’s lived with this all her life. If she wanted to try regressive hypnosis she could have by now. It’s not always accurate. It can both fail to bring out things the person “should” know (like a compete license number), it can also produce false memories. Maybe she doesn’t want her most vivid memories of her parents to be of violence, especially when retrieving them still might not lead to a prosecutable case after 33 years. It’s HER choice. Crystal, if you see this, I wish for you a happy and satisfying life.

      Reply

  10. Avatar

    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?

    Reply

    • Avatar

      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.

      Reply

  11. Avatar

    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.

    Reply

  12. Avatar

    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.

    Reply

  13. Avatar

    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.

    Reply

  14. Avatar

    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….

    Reply

  15. Avatar

    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.

    Reply

    • Avatar

      Catrina

      They can’t do DNA analysis if no sample was saved from 1985. Obviously a test was done, since the bloodstains were too degraded for A/B/O typing, but if it couldn’t be used for evidence they probably threw it out. LEOs at the time had no idea DNA analysis was coming. In 1985 I was studying grad-level genetics and had a peeping tom. Cops came, took it seriously, very polite, and we discovered the perp had dropped a personal item right outside my window. Knowing from my studies that DNA would be useful in the near future for forensics, and peeping toms often become rapists, I asked the cops to preserve the item, knowing it could tie the guy to later cases, but they’d never heard of DNA, didn’t believe me.

      Reply

  16. Avatar

    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!!

    Reply

    • Avatar

      Anonymous

      As long as people like you vote here

      Reply

    • Avatar

      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.

      Reply

    • Avatar

      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.

      Reply

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