Michael (Chad) Boysen, 26, is the suspect in the murder of his grandparents on Friday night, said Sgt. Cindi West with the King County Sheriff's Office.
Detectives have been told that Boysen may be trying to get additional weapons because evidence showed Boysen searched the internet for information on gun shows across the Pacific Northwest and Nevada, West said.
Boysen is now considered "an extreme danger to the public and police," West said.
Boysen was last heard from on Friday night when he was at the victims' Fairwood home in the 16200 block of 145th Ave. SE, West said. On Saturday, the victims' daughter discovered their bodies after becoming concerned they could not be reached.
Family members identified the couple as Robert R. and Norma J. Taylor. They were both in their early 80s.
Detectives are also searching for the couple's car that is missing from the home. It is a red 2001 Chrysler 300 with Washington license plate number 046-XXU. They believe Boysen may be driving the car. A photo of the car shows there may be a memorial ribbon magnet attached to the trunk.
Boysen was released from prison on Friday after serving a sentence for a residential burglary conviction. His criminal history includes felony convictions for robbery. Boysen is 5-feet-10-inches tall and weighs about 170 pounds.
West asked anyone who sees Boysen or the Chrysler to call 911 immediately.