The young man who killed six people at a house party over the weekend had brought three guns, more than 300 rounds of ammunition, a baseball bat and a black machete, and told guests as he blazed away, "There's plenty for everyone," authorities said Monday.

Aaron Kyle Huff, 28, was "clearly intent on doing homicidal mayhem," Deputy Police Chief Clark Kimerer said.

However, investigators still have no idea why, he said.

"We may be asking these questions over the next year or two," Kimerer said. "Hopefully we will find some answers."

Huff committed suicide when confronted by an officer outside the house early Saturday. Toxicology results will not be available for several days, Kimerer said.

Police said the victims, many of them dressed up as zombies in black with white face paint, had met Huff earlier in the night at a rave called "Better Off Undead" and invited him to a party at their rented home.

Huff left the party at about 7 a.m. and returned wearing bandoliers of ammunition and carrying a 12-gauge pistol-grip shotgun and a handgun.

As he walked back to the party, Huff used spray paint to write "NOW" on the sidewalk and a neighbors' stairs, police said.

He killed two people on the front steps, then killed three more people in the living room and went looking for more victims, police said.

He tried to enter a locked bathroom, jiggled the handle and fired a few rounds through the door, missing a frightened couple.

As shots rang out, neighbors called 911. When police confronted Huff, he put the shotgun in his mouth and pulled the trigger.

"What he might have done if he was able to leave this scene and continue this rampage, I shudder to contemplate," Kimerer said.

At a news conference, detectives displayed an assault rifle, baseball bat and machete seized from Huff's pickup truck. He had more than 300 rounds of ammunition, Kimerer said. The detectives said they seized additional weapons from the apartment he shared with his twin brother, but did not describe them.

The attack was "clearly a premeditated and well-planned assault on innocent people," Kimerer said earlier. "It is very clear that he had thought out a murderous spree, a campaign."

Police determined that Huff's twin knew nothing of his brother's intentions. Huff had delivered pizzas during the five years he lived in Seattle.

They were "twin teddy bears," Regina Gray, manager of Town & Country Apartments, said Sunday. "He and his twin brother are the kindest, sweetest, gentlest people."

But James Winn, 20, of Seattle, said Huff was "quick to anger."

"Someone would say one thing and he'd snap and walk away," Winn said at the makeshift memorial at the crime scene, recalling when he spent time with Huff and his brother near the boys' family home in Whitefish, Mont.

No altercations or arguments were reported at the party, Kimerer said.

The King County medical examiner released names of the dead Monday: Melissa Lynn Moore, 14; Suzanne Thorne, 15; Christopher Williamson, 21; Justin Schwartz, 22; Jason Travers, 32; and Jeremy Martin, 26.

Two people wounded in the shooting were in satisfactory condition.