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Catching a killer: How Tacoma police used genetic genealogy to crack 1986 cold case

New DNA technologies may finally bring justice to a Tacoma murder 32 years later.
12-year-old Michella Welch went missing on March 26th, 1986. Her body was discovered later the same day in Puget Park. Credit: Tacoma Police Department Child Abduction Response Team

Michella Welch was just 12 years old on March 26, 1986, when she was raped and murdered in a park near her Tacoma home. After an initial investigation led to no arrests, the case went cold. Now, 32 years later, new DNA technologies may finally bring Michella justice.

On Friday, Tacoma police, the Pierce County Prosecutor’s Office, and the mayor of Tacoma announced the arrest of 66-year-old Gary C. Hartman for the rape and murder. They say the break in the case was made possible by genetic genealogy, a tool that has recently led to arrests in such high-profile cases as the Golden State Killer.

“This was the crossroads of good, old-fashioned police work and new technology,” said Tacoma Police Chief Donald Ramsdell.

Police had previously constructed a DNA profile of the killer from crime scene swabs but were unable to find a direct match through the FBI’s national DNA database.

Traditional DNA tests rely on matching mitochondrial DNA, which is passed to a child only from its mother, or Y-chromosome DNA, passed only from the father. They look for short tandem repeats, or STRs, which are repeating segments of DNA that differ from person to person. STRs can only reveal parent/child or direct sibling relationships.

Genetic genealogy instead uses autosomal DNA, or aDNA, which is inherited from both parents. aDNA tests look for single nucleotide polymorphisms, or SNPs. These are changes at a single point in DNA that occur in whole populations. This means that SNPs can reveal connections between distant relatives.

Parabon Nanolabs, a company at the forefront of genetic genealogy, says they can distinguish between 6th-degree relatives (second cousins once-removed) and unrelated strangers with greater than 98 percent accuracy.

To find related individuals, genetic scientists compare strands of DNA and look for long sections that match between the two. The more matching segments and the longer these segments are, the more closely related two people are.

In the Welch case, Parabon analyzed the aDNA from decades-old crime scene swabs and compared it to a public DNA database. These databases have ballooned in popularity with the rise of at-home DNA testing. More than 12 million people have had their DNA tested for genealogical purposes.

When Parabon uploaded the newly-constructed profile to the database, a “significant match” was found, according to court documents. This allowed investigators to construct a family tree through traditional sources such as marriage and death certificates. Two brothers were identified as suspects due to their age and location at the time of the murder.

Once they had identified the suspects, Tacoma police reverted to more traditional police work. They obtained DNA from a discarded napkin and used a traditional STR test to compare it to the DNA on file. It was a match.

The match was made on June 19, 2018, and the police arrested Hartman on June 20. Tacoma Police Department confirms that Hartman was never a person of interest in the investigation until he was identified through genetic genealogy.

Related: Suspect charged in 1986 murder of Tacoma girl

Prosecutors and police hope genetic genealogy will help them crack open more cold cases as the technology continues to develop.

“If you think you can run, you’re wrong. If you think you can hide, you’re wrong,” warns Ramsdell. “If you think Tacoma Police Department is going to give up, you’re wrong.”

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