Daniel Jay Perez, 26, now faces a life term without the possibility of parole under the state's three strikes law.
Sentencing is set for Nov. 8.
A jury deliberated several hours Friday afternoon and reached its verdict before noon on Monday.
Perez was convicted of attempted second-degree murder and second-degree assault for trying to strangle fellow inmate David Hindal in November 2009 in the laundry room of special offenders unit at the Monroe Correctional Complex.
That day, Hindal was reading a book and performing his duties in the laundry room when Perez snuck up behind him. Perez wrapped a strip of cloth around his neck and pulled until Hindal lost consciousness, according to court records.
Perez left the room and returned to his cell.
When Hindal regained consciousness, he emerged from the laundry room and waved at the corrections staff.
The laundry room was a "blind spot," meaning that it can't been seen on the prison's video system.
Cameras, however, captured Perez in an adjacent day room. The video showed him pacing back and forth along one wall. After a couple of minutes Perez was seen pulling a ligature from his pocket and stretching it between his hands as he approached the laundry room
After the assault, Perez told corrections officers that God was making him do things and he began to yell about Satan, court papers said.
The case became more challenging to argue shortly before trial when Hindal said he would not testify, deputy prosecutor Tobin Darrow said.
"We had to go forward without testimony from the victim," Darrow said.
Perez originally was sent to the Washington State Reformatory in 2005 after he was convicted of vehicular homicide, vehicular assault and theft in Pierce County. About seven months into his sentence, Perez strangled his cellmate, Cory Garzina, with the drawstring from his prison-issued sweatpants. Garzina was found dead in the cell. He was serving a 14-month sentenced and was due to be released the next month, court papers said.
Perez told investigators that he'd had a dream that Garzina was going to stab him so he decided "he was going to take action first," according to court documents.
A jury in 2008 found Perez guilty of second-degree murder and he was sentenced to 30 years for the slaying.
Following the conviction, Perez continued to be housed in the special offenders unit at Monroe but no longer shared a cell.
Eric Stevick: 425-339-3446; email@example.com.
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