(Reuters) - Police hunting for an ex-convict accused of killing his grandparents after they threw him a party to celebrate his release from prison surrounded a motel in Oregon as they sought to narrow their search for the fugitive, a sheriff's spokeswoman said on Tuesday.

Michael "Chadd" Boysen, 26, is suspected by police of killing his grandparents in Renton, Washington, and stealing their car.

"We have information that Boysen may be in a motel room in Lincoln City, Oregon," Cindi West, a spokeswoman for the King County Sheriff in Washington state, said in an email. She said a SWAT team was at the motel.

Lincoln City is 76 miles southwest of Portland on the Oregon coast and has a population of about 8,000.

Police said on Monday that Boysen had planned to target people in positions of authority.

"We need to do everything we can to get this man off the street as soon as possible," King County Sheriff John Urquhart said in a statement on Monday. "His threats against authority figures make him very dangerous and unpredictable."

Boysen was released from prison on Friday after serving a nine-month sentence on a burglary conviction. He had been incarcerated at the Monroe Correctional Facility in Washington state.

Police said the grandparents had given Boysen a room in their home. They picked him up from prison on Friday, helped him get a Washington state identification card and hosted a family party later that evening, police said.

Boysen's mother found the bodies of her parents on Saturday, according to police. The next day, the King County Sheriff's Office issued a warrant for Boysen's arrest.

(Reporting by Laura L. Myers in Seattle, Writing by Alex Dobuzinskis; Editing by Cynthia Johnston)