KPTV-TV, Portland, Ore., reported police officers entered a room at the Westshore Oceanfront Suites in Lincoln City, Ore., about 7 p.m. local time and found Michael "Chadd" Boysen, 26, on the floor with visible injuries. Investigators said they were self-inflicted cut or stab wounds, the TV station said.
Boysen was taken to a hospital to be treated for his injuries before being arrested.
Investigators said Boysen checked in to the motel under his real name Monday night and police showed up Tuesday morning, evacuating the other rooms, as well as homes in the area.
Police said they tried to negotiate with Boysen and had set off flash-bang grenades in an attempt to flush him out, The Seattle Times reported.
Police then remained in a "holding pattern" for several hours until finally moving in and making the arrest, the newspaper reported.
Westshore Oceanfront Suites owner Kent Landers said his employees recognized Boysen's name from a television news report as that of a man who checked into the hotel Monday night, the Times reported.
Sheriff's detectives said Boysen was a danger to police and the public.
Boysen's grandparents -- Robert, 82, and Norma Taylor, 80 -- were found dead in their Renton home Saturday, two days after Boysen completed a nine-month prison sentence for breaking into a home. The victims were last seen alive at a welcome-home party for Boysen in their home, where they had prepared a place for him to stay, seattlepi.com reported.
A warrant was issued for his arrest in connection with the deaths, which police said were being investigated as homicides. No details of how they died have been released.
King County, Wash., Sheriff John Urquhart said Monday the victims picked Boysen up Friday when he was released from the Monroe Corrections Complex, where he had served a sentence for attempted residential burglary. They took him to meet his probation officer and helped him get identification card from the Department of Licensing, Urquhart said.
He said Boysen had made threats against law enforcement officers in the past and is attempting to obtain weapons to kill citizens, corrections officers and police.