A gunman who killed six people at a rave party last March passed up opportunities to shoot more people and may have lost interest during the rampage, according to a report released Monday.

Kyle Huff, 28, passed up chances to kill two people cowering in a bathroom, someone who was sleeping in plain view, and several others who were poorly hidden behind furniture, said the report by an investigative panel.

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He had two guns and hundreds of rounds of ammunition, the report said. As he walked through the house where the shooting took place, he repeatedly pumped his shotgun even though it was ready to fire, ejecting unspent shells.

"It was as if he had lost interest in shooting any more, or it was just too much effort," the report said. "It may be that whatever satisfaction he had hoped to derive from the shooting spree was not forthcoming or had been satiated."

Huff killed himself when he was confronted by a police officer. His suicide precluded the need for a police investigation, but the Seattle Police Department asked James Alan Fox, an expert on mass murders from Northeastern University, to assemble a four-member panel to study the case.

Fox and Police Chief Gil Kerlikowske told about 80 people at a community meeting Monday that there was no single factor that triggered the shooting, and that Huff had been planning it for at least days, and probably weeks.

"It wasn't a sudden explosion of rage," Fox said.

The panel's report said Huff's life was a series of frustrations, from his parents' divorce to his poor grades, his difficulty relating to women and his envy of his more successful brother.

He left his few friends in Whitefish, Mont., behind when he moved to Seattle with his twin brother in 2002. Huff likely turned to Seattle's welcoming rave community for friendship, but apparently even there he did not fit in, the report suggested, and he came to view the rave lifestyle, including drug use and promiscuity, as a threat.

On the eve of the shooting, Huff headed to a zombie-themed rave and was invited to an after-party at the house in the Capitol Hill neighborhood.

"There is no evidence, of course, that Huff was actually mistreated in any way," the report said. "However, if he were indeed made to feel different, his response, given his existing attitude about raves and ravers, would be explosive."

Kyle Moore, father of 14-year-old victim Melissa Moore, said the report was largely speculation. "There's no answer," he said. "We'll never know."