CNN — (CNN) -- Washington police continued their manhunt early Tuesday for a 26-year-old man who allegedly killed his grandparents over the weekend, shortly after they held a party to celebrate his release from prison.
Michael Boysen was released Friday from the Monroe Correctional Facility, where he served a year behind bars for burglary.
His grandparents picked him up, drove him around running errands, and held a gathering for family members at their home to welcome him back, said King County Sheriff John Urquhart.
The next day, the grandparents were found dead.
After Boysen and his grandparents did not respond to phone calls Saturday, his mother drove over with a key to the house in Renton, near Seattle, and found the couple's bodies.
Boysen and his grandparents' car were missing. Police started a manhunt.
Authorities have not said how the victims were killed. A gun was not used, but the deaths were violent, they said.
During the course of their investigation, detectives said they learned that Boysen had talked about killing his grandparents, acquiring guns and going after authority figures. He had searched in the Internet for gun shows across the Pacific Northwest and Nevada.
"We need to do everything we can to get this man off the street as soon as possible," Urquhart said. "His threats against authority figures make him very dangerous and unpredictable."