Suspect identified in 1990 cold case murder of Seattle teen

Detectives with the Snohomish County Sheriff’s Office have identified a suspect in a 1990 cold case murder of a 17-year-old Seattle girl, the sheriff’s office announced Thursday.

The suspect, Robert A. Brooks, was identified through investigative genetic genealogy, the sheriff’s office said. He died in King County on Oct. 26, 2016.

According to the sheriff’s office, Brooks had been released from prison on April 18, 1990, just four months before the body of 17-year-old Michelle Koski was found by a woman walking her dog at Highway 522 and Echo Lake Road in Snohomish on August 25, 1990.

Koski had last been seen on August 18, 1990 near her house in the 13300 block of 30th Ave Northeast in Seattle.

Brooks was living with a relative in the 12500 block of 25th Avenue Northeast in Seattle at the time, just a few blocks from where Koski lived, according to the sheriff’s office.

“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 2005, Detective Jim Scharf and retired Detective David Heitzman were assigned to the sheriff’s office’s newly formed cold case team and Heitzman took the lead on the case at the time.

There was no DNA match in the national database and the case remained cold over the next decade.

Brooks was identified with help from Parabon NanoLabs and genetic genealogist Deb Stone, the sheriff’s office said. The crime scene sample that detectives sent to Parabon was a mixture of DNA between the suspect and the victim.

Parabon was able to “deconvolute the mixture and ensure that the matches would lead to a perpetrator,” the sheriff’s office said.

A digital file with DNA genotype data was uploaded to a public genetic genealogy website and Stone worked for approximately one year building family trees, ultimately leading to the identification of two brothers.

With 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 Brooks that positively matched the DNA from the crime scene.

According to the sheriff’s office, the estimated probability of selecting an unrelated individual from the U.S. population with a matching DNA profile is one in 1.2 quadrillion.

“Thousands of hours have gone into the Michelle Koski homicide investigation,” said Detective Heitzman. “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.”

Anyone with information related to the case or the suspect is asked to call the Snohomish County Sheriff’s Office tip line at 425-388-3845.