Police pointed rifles at a motel on the Oregon coast and used loudspeakers Tuesday afternoon as they tried to persuade a man believed to have killed his grandparents last weekend to surrender.

Michael Boysen has been the subject of a multi-state 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.

Three loud bangs were heard at the Westshore OceanFront Suites in this tourist town early in the afternoon. It wasn't immediately clear what caused the noise.

Before and after the bangs, police used a loudspeaker to try to persuade the person inside a room at the motel to disarm and surrender. The voice on the loudspeaker said, "There's a lot of people who want to see you come out OK."

Police had sent a small robot up some stairs and onto a balcony of the motel before the blasts.

Rooms at the Oregon motel were 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.

Its owner, Kent Landers, told The Oregonian newspaper that one of his property managers checked Boysen in under his own name on Monday night.

"It wasn't an alias," Landers said. "How stupid is that?"

The manager didn't recognize the name, Landers said, but on Tuesday morning she saw a television story, recognized the face and called Lincoln City police.

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 have 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," West said. "It's just bizarre. The family loved and supported him the whole time he was in prison."

The King County medical examiner's office has not released their names. Family and neighbors told KOMO News they are Robert R. Taylor, 82, and Norma J. Taylor, 80.

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