Prosecutors filed 12 counts of first-degree murder Thursday against a woman they say started a deadly hotel blaze by setting a mattress on fire after a dispute with a fellow tenant.

Valerie Moore, 47, a convicted murderer who was paroled a year ago, was arrested the morning after the Oct. 31 fire but had been held on a parole violation while authorities searched for bodies — a process that took until Wednesday because the gutted building was so hazardous.

The fire at the 84-year-old, $150-a-week Mizpah Hotel was Reno's deadliest ever, killing 12 people and injuring 31.

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The criminal complaint also includes one count of first-degree arson, said Dave Clifton, Washoe County's chief deputy district attorney.

"This was a horrendous fire and devastating to life. We're going forward with full vigor to get justice in this case," Clifton said.

He declined to discuss any of the evidence recovered from the historic, three-story brick building "because it's too big of case as far as all the potentials, the death penalty and so on."

Moore, who worked at a nearby casino, will make her initial appearance Monday, Clifton said. The county public defender's office has been assigned to represent Moore, he said, but an attorney has not been designated.

As many as 83 tenants were in the Mizpah Hotel when the fire broke out, police said. Many were rescued by firefighters on ladders, and several jumped to the street below.

A national response team from the Bureau of Alcohol, Tobacco, Firearms and Explosives worked with local crews using search dogs and state-of-the-art equipment to recover the victims. The building was so badly damaged that parts had to be shored up before they could be searched.

Moore was paroled last year after serving 17 years in a Nevada prison for second-degree murder for killing an unemployed Reno waitress in 1987. Witnesses at the hotel said Moore had been drinking and apparently flew into a rage the night of the fire after quarreling with a fellow hotel resident.