SEATTLE (AP) – A man already serving two life sentences for murder has been charged with committing what prosecutors say is Washington state’s oldest unsolved crime, the 1968 fatal stabbing of a pregnant teenager.

John Dwight Canaday, 59, admitted recently during questioning by Seattle police detectives that he killed Sandra Bowman, according to charging papers filed Thursday.

Canaday sighed, held up his hands and declared, “Yes, I killed her,” when told he had left DNA at the scene, the documents said.

A prisoner at the Walla Walla penitentiary, Canaday faces another possible life sentence for the Bowman slaying. He is scheduled to be arraigned Wednesday.

Earlier this year, a state forensic scientist matched Canaday’s DNA to sperm found on Bowman’s body. His genetic profile was in the database because of two 1969 murder convictions.

Bowman, who was in her second trimester of pregnancy, was stabbed at least 57 times. The 16-year-old was found by her husband when he came home from work – face down on their bed, her hands tied behind her back.

Canaday was working as a pipeman’s helper for the city water department when Bowman was killed.

In a June interview, according to the documents, Canaday told the detectives that he “randomly knocked on her door” and “attacked her … I stabbed her.”

The charging papers said Canaday blamed the December attack on a bitter divorce, “a lot of anger at myself and immaturity.”

In court documents, Deputy Prosecutor Timothy Bradshaw said killing Bowman “evidently emboldened” Canaday to attack other women, killing two of them.

In January 1969, Canaday kidnapped and strangled 21-year-old Mary Bjornson. Three weeks later, he raped and killed Lynne Tuski, 20.

Canaday was sentenced to die for those murders but won a reprieve in 1972 when the Supreme Court struck down the death penalty in more than 30 states, including Washington.

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