SEATTLE - Authorities are searching the Northwest for a man accused of killing his Seattle-area grandparents, who had just picked him up after his release from a Washington state prison, hosted a party in his honor and offered him a room in their home for the night.

Michael "Chad" Boysen, 26, is considered extremely dangerous and has tried to obtain guns, police said Monday.

He was released from prison Friday after serving several years for robbery. His grandparents - an 82-year-old man and 80-year-old woman - picked him up from prison and hosted a family "welcome home party" for him that night, King County Sheriff John Urquhart said.

The grandparents were killed later Friday or early Saturday at their Renton home. Authorities believe Boysen also stole their car.

"I can't stress how dangerous this guy is," Urquhart said at a news conference. The sheriff said Boysen had made threats against family members and law enforcement officials, but he did not elaborate.

"We have to catch him as soon as we can," Urquhart said.

The sheriff said the grandparents were not shot, but he declined to provide other details about their killings, pending autopsies.

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. He was released Friday from the prison at Monroe, about 35 miles north of Renton, and was supposed to check in with a community supervision officer within 24 hours, she said.

Boysen's grandparents had fixed up a room in their home for him to sleep in his first night out of prison, said Sgt. Cindi West, a sheriff's spokeswoman. 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 5-foot-10, weighs 170 pounds and has hazel eyes. 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.

Autopsies on the victims were scheduled for Monday and their names will be released later, the King County medical examiner's office said.

Friends and family identified the elderly 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.

When a family member became concerned that the Taylors didn't answer their door, the daughter was called and found their bodies about 7 p.m. Saturday.

It's really scary that it happened two doors down," Smith told KIRO-TV.

"We were home Friday evening, and we left the house about 2 in the afternoon on Saturday. And when we came home, about 8 o'clock, it was full of police cars."