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Suspect Identified in 1990 Homicide Cold Case 




SNOHOMISH COUNTY, Wash. – Detectives from the Snohomish County Sheriff’s Office have identified a suspect for the 1990 murder of 17-year-old Michelle Koski. Her body was found on August 25, 1990, by a woman walking her dog at Highway 522 and Echo Lake Road in Snohomish. The suspect, Robert A. Brooks, was identified through investigative genetic genealogy. Brooks died in King County on October 26, 2016. He was released from prison on April 18, 1990 and was living with a relative in the 12500 block of 25th Ave NE in Seattle, just a few blocks from where Michelle lived. 


“After more than 30 years of searching for answers following this terrible murder, we can finally provide Michelle’s family with some answers,” said Snohomish County Sheriff Adam Fortney. “Thanks to the relentless persistence of our cold case detectives, new DNA technology and advancements in genetic genealogy, we are now able to solve cases we once thought we’d never find answers to.”


In February 2005, Detective Jim Scharf and retired Detective David Heitzman were assigned to the newly formed Cold Case Team.  Retired Detective Heitzman selected Michelle Koski’s case as the primary case he was taking the lead on at that time. There was no DNA match in CODIS, and over the next decade, several suspects were ruled out by obtaining their DNA. The case remained cold.  


The suspect, Robert A. Brooks, was identified using Investigative Genetic Genealogy; the use of DNA testing in combination with traditional genealogical methods to establish the relationship between an individual and their ancestors.  

Successful identification of Brooks was established with assistance from Parabon NanoLabs and genetic genealogist Deb Stone. The crime scene sample detectives sent to Parabon was a mixture of DNA between the perpetrator and the victim. Due to Parabon's Bioinformatics work, they were able to deconvolute the mixture and ensure that the matches would lead to the perpetrator.

A digital file containing DNA genotype data was uploaded to Family Tree DNA and GEDmatch, a public genetic genealogy website. Genealogist Deb Stone, from Kin Forensics, worked for approximately a year building family trees which ultimately led to the identification of two brothers.  

The suspect, Robert A. Brooks, was born on April 25, 1967.  He died on October 26, 2016, from natural causes. With the cooperation of the Snohomish County and King County Medical Examiner’s Offices and the Washington State Patrol Crime Lab, a blood sample was tested from Robert Brooks that positively matched the DNA profile from the crime scene evidence. The estimated probability of selecting an unrelated individual at random from the US population with a matching profile is one in 1.2 quadrillion. 

If you or anyone you know has information related to this case or the suspect, please call the Snohomish County Sheriff’s Office tip line 425-388-3845.



News release from Parabon NanoLabs:

Parabon Rescues Profile from Mixed DNA to Enable Improbable Solve

Case background:
On August 25, 1990, 17-year-old Michelle Koski’s body was found near Highway 522 and Echo Lake Rd. She was last seen near her house in the 13300 block of 30th Ave NE in Seattle on August 18, 1990. Earlier that day, Michelle had been at an apartment in the 6200 block of 14th Ave NW in Seattle.  


A person with long hair

Description automatically generated with low confidence

Michelle Koski 


Statement regarding the Michelle Koski murder:

 “This is a fitting finish to Detective Scharf’s distinguished career being the voice for those no longer able to speak for themselves.  The epitome of a homicide detective, he has effectively set the bar very high for cold case investigations in the State of Washington.


Thousands of hours have gone into the Michelle Koski homicide investigation.  The initial investigators laid a solid foundation with the proper collection and preservation of evidence, so that as the DNA technology improved years later, Cold Case Unit investigators working with the WSP Crime Lab, were able to have that evidence analyzed to ultimately identify Michelle’s killer. It was a privilege to have been part of the team that worked on this case, and very rewarding to have it resolved.


There are currently over 2,200 unsolved missing and murdered cases in the State of Washington.  It is paramount for law enforcement to invest resources into the investigation of these “cold cases”.  The commitment of the Snohomish County Sheriff’s Office in solving homicide cases has been evident since the Cold Case Team was created in 2005. I am grateful that every Snohomish County Sheriff since then has maintained the integrity of the office by continuing to staff this important mission. 


It is my hope and prayer that the resolution of this case will bring some measure of peace to the family and friends of Michelle Koski.”

 - David Heitzman, Retired SCSO Cold Case Unit Detective (2005-2009)