King CountySheriff's detectives believe a woman found in the trunk of a burned car last week was beaten and strangled to death by two suspects.

Kennon Fastrup and Michelle Backstrom were arrested Saturday following a vehicle pursuit, detectives said. The body of Denise Grigsby, 39, was found May 6 off Auburn-Black Diamond Road.

According to probable cause court documents, Grigsby and Fastrup got into a physical argument at Backstrom's house in Kent on May 4 or 5. Police said Backstrom intervened but then began beating Grigsby after Grigsby hit her.

Police believe Fastrup then repeatedly hit Grigsby in the head with a metal object.

Detectives said Grigsby was strangled with a metal rope and nylon lanyard cord then placed in the trunk of her car. The two suspects allegedly drove the car to Auburn-Black Diamond Road and lit it on fire before fleeing the scene.

According to court documents, Fastrup was dating both Grigsby and Backstrom at the time. All three are suspected of using methamphetamine.

Fastrup and Backstrom are expected in court for a bond hearding Monday afternoon.

KING 5's Lindsay Chamberlain compiled this report.

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