EVERETT, Wash. -- A jury in Washington state convicted an inmate of first-degree aggravated murder Thursday in the strangulation of a female prison guard.

The Snohomish County jury must now decide whether to sentence 54-year-old Byron Scherf to the death penalty.

Scherf is a convicted rapist who was serving a life sentence when he killed 34-year-old Jayme Biendl in January 2011.

The defense didn't dispute that he strangled the corrections officer with an amplifier cord in the prison chapel of the Washington state Reformatory at Monroe.

His lawyers had suggested he didn't plan to kill Biendl, and said he blacked out in the final minutes of her life.

The jury saw Scherf's video confession this week and heard forensic testimony about how Biendl was strangled. Scherf said he first planned to ambush and beat up Biendl over something she said to him. He refused to say what set him off.

The Everett Herald reports that (http://bit.ly/ZT0IQI) it took the jury less than an hour to convict Scherf, following a trial that began May 1.

He initially cooperated with investigators and confessed but stopped because he says he was denied jail privileges that had been promised.

On Wednesday, Snohomish County Medical Examiner Norman Thiersch testified it would have taken four to five minutes of constant pressure to strangle Biendl. It took significant force to fracture the cartilage in her neck while she struggled to survive, he said.

Scherf's DNA was found on Biendl's fingernails. His blood was found on her coat and the amplifier cord, forensic scientists from the state crime lab testified.

Scherf's hands were bright red with an obvious mark across a palm, testified a Monroe police detective who saw him a few hours after the killing.

Scherf said he blacked out while pulling on the cord. When he came to, he was sitting in a chair in the back of the church sanctuary. He told detectives he had no memories of Biendl dying.

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