Police stormed a motel room in a seaside town Tuesday evening and captured a Washington state man suspected of killing his grandparents, ending a multistate search and a tense daylong standoff at the motel.

Officers found Michael Boysen lying on the floor on his back with apparently serious self-inflicted cuts, Lincoln City police Chief Keith Kilian said.

The 26-year-old man was flown to Legacy Emanuel Medical Center in Portland.

Hospital spokeswoman Judy Pahl described his condition as critical shortly after he arrived late Tuesday night.

No officers were hurt in the standoff, which Kilian termed "very successful." Law enforcement officials in Washington state had described Boysen as extremely dangerous.

Michael Boysen has been the subject of a multistate manhunt since Saturday, when the bodies of his grandparents were found in their suburban Seattle home. Washington state authorities have said Boysen killed the couple the day after they threw a welcome home party for him after his release from prison.

After negotiations with the man holed up inside the Westshore OceanFront Suites in this tourist town went nowhere on Tuesday, police used three blasts from a water cannon to break a window at the motel because "the guy had been quiet for too long," said Lincoln City Police Chief Keith Kilian.

"There was a lack of activity going in there, so we did a strategic breach, which caused conversations to be continued," Kilian said. "We weren't progressing, so we stepped it up a little bit."

A state police negotiator used a bullhorn to try to persuade the person inside the second-floor motel room to disarm and surrender. The voice on the loudspeaker said, "There's a lot of people who want to see you come out OK."

At one point police officers were seen going into an adjacent room. Earlier in the day, police had sent a small robot up some stairs and onto a balcony of the motel.

Rooms at the motel were quietly evacuated and surrounding streets were closed off. Nearby residents were told to remain in their homes, and a growing number of officers converged on the motel.

Boysen checked into the motel Monday night under his own name, but the name wasn't recognized until Tuesday morning when a desk clerk saw a television story about the case and called the Lincoln City police, Kilian said.

A State Police negotiator used a bullhorn to talk to the man, but hadn't made headway.

"He asked for us to leave, that's about it," Kilian said.

Officers haven't seen the man display any weapons, he said.

Boysen, 26, made threats against members of his family and law enforcement while behind bars, Corrections Department spokesman Chad Lewis said Tuesday. But authorities didn't learn of the threats until after the bodies of the grandparents were found and authorities had started looking for Boysen.

"Sources went to our staff at the Monroe Correctional Center and told us he had been threatening to do all this," Lewis said.

The information was passed on to King County deputies, and that's why King County Sheriff John Urquhart called Boysen extremely dangerous at a Monday news conference.

Boysen just finished serving nine months in prison on a burglary conviction, Lewis said. He had no violent infractions in prison — "nothing extraordinary," Lewis said.

He served a previous sentence between 2006 and February 2011 for four robbery convictions. Those convictions were related to an addiction to narcotic painkillers, Lewis said.

Boysen's grandparents picked him up from prison in Monroe on Friday, drove him to meet his probation officer and to get an identification card from the Department of Licensing. They held a welcome home party for him Friday night.

The bodies were discovered by Boysen's mother Saturday evening. She had been called by a family member who became concerned that the couple hadn't answered their door.

Authorities haven't said how they died. Investigators determined that Boysen had been searching the Internet for gun shows.

The motive for the killings remains unknown, King County sheriff's Sgt. Cindi West said.

"Between the family and detectives we have no idea," she said. "It's just bizarre. The family loved and supported him the whole time he was in prison."

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The King County medical examiner's office hasn't released their names. But family and neighbors told KOMO News they are Robert R. Taylor, 82, and Norma J. Taylor, 80.

Associated Press writers Jeff Barnard in Grants Pass, Ore., and Doug Esser in Seattle contributed to this report.