A convicted felon is on the run after allegedly killing his grandparents as they hosted a party to celebrate his release from a Washington state prison. 

Michael "Chad" Boysen, 26, is considered extremely dangerous and has tried to obtain guns, police said Monday. Q13 Fox reports Boysen has also made threats against law enforcement and community leaders, according to police. 

Boysen was released from prison Friday after serving several years for robbery. His grandparents, 82-year-old Robert Taylor and 80-year-old Norma Taylor, picked him up from prison and hosted a family "welcome home party" for him that night, Q13 Fox reports.

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

"This is an exceedingly heinous crime any way you look at it, and I think the risk that's out there is extreme right now," King County Sheriff John Urquhart told Q13 Fox. 

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.

"Basically right now we have a person that's very, very dangerous on the run that we believe is trying to obtain weapons to kill citizens and police officers and corrections officers," Urquhart told Q13 Fox.  "We need to catch this guy."

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.

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The Associated Press contributed to this report.