US law enforcement blew the roof off a mountain hideout in Washington state on Saturday and inside found the body of a man suspected of killing his wife and teenage daughter, officials said.

Peter Keller, who had been missing since Sunday when the bullet-ridden bodies of Lynnettee Rocha Keller, 41, and their 19-year-old daughter Kaylene Keller were discovered at the family home, apparently died of a self-inflicted gunshot wound.

"They believe the person has been dead for some time. There's a great deal of blood and a pistol nearby," King County Sheriff Steven Strachan said of the scene in the Cascade foothills 40 kilometers east of Seattle.

Evidence led investigators to the mountain bunker late Friday and a SWAT (Special Weapons and Tactics) team fired tear gas into the structure and stood guard at the site overnight.

But on Saturday, they used explosives to blow off the bunker's roof, leading them to Keller's body. The bunker had been fortified by logs and dirt and was believed to stretch back at least six meters into the mountainside.

"They were able to make a big enough hole where they could look in and saw what was a body, that appeared to be possibly a self-inflicted gunshot wound," King County sheriff spokeswoman Katie Larson told AFP.

"We had our bomb disposal unit clear the bunker to make sure there are no booby traps or explosives in there from him."

She said police would have preferred to take Keller alive, but were relieved that there was not a potentially deadly shootout with officers.

"All of us here were extremely worried and nervous that this guy was as armed as he was, and we actually now know he was, would have shot and injured or killed some of our officers," Larson added.

"The outcome being none of our people got hurt that way, it makes us happy."

Keller, 41, was named a suspect Wednesday in the murder of his wife and daughter, whose bodies were found after neighbors called the authorities when they noticed the home had been set on fire.

Investigators have yet to establish a motive for the killings, according to the King County Sheriff's Office.

"It would have been nice if we could have taken him alive to so we could try to find out exactly why he killed his wife and daughter, and get more information out of him, but, unfortunately, that was not the case," Larson said.

ABC News reported that Keller, a reputed survival skills enthusiast, had spent eight years planning and building the bunker, pictures of which police said he intended to destroy in the fire at the family home. (AFP)