Friends and family identified the couple to TV stations as Robert R. and Norma J. Taylor. They were members of the local Church of Jesus Christ of Latter-day Saints, neighbor Ronna Smith told KOMO-TV.
Detectives believe Boysen is trying to find weapons, and Urquhart said authorities do not believe he had a gun when he left the crime scene. Boysen had been searching the Internet for "gun shows" across the Northwest and Nevada, the sheriff's office said.
Boysen had been in prison since 2006 on three robbery convictions in King County, said Judy Feliciano of the state Corrections Department.
Boysen's grandparents had fixed up a room in their home for him to sleep in his first night out of prison, West said. Boysen was planning to stay elsewhere after that.
"We are at a loss as to why he killed them," Urquhart said. "We don't know what the motive is."
Boysen is white, 5-foot-10, about 170 pounds and has hazel eyes and brown hair in a photo released by police. He may be driving his grandparents' red, 2001 Chrysler 300, with Washington license plate 046XXU.
A warrant has been issued for Boysen's arrest. If he's stopped anywhere in the country, law enforcement officers will know he's a wanted man, state Corrections Department spokesman Chad Lewis said.