A major power company is responsible for the deadliest wildfire in California history, an investigation by the state fire agency Cal Fire has found.

The Camp fire, which killed 85 people and almost completely incinerated the town of Paradise, was sparked by transmission lines owned by Pacific Gas & Electric in the early morning of 8 November last year, investigators concluded. “Tinder dry vegetation” and high winds “caused extreme rates of spread”, Cal Fire said in a statement.

“It brings some finality,” the Paradise mayor, Jody Jones, told the Guardian about Cal Fire’s conclusions.

PG&E filed for bankruptcy in January, facing billions of dollars in liabilities over multiple disasters in the state, and admitted at the time that its lines were the likely source of the Camp fire.

The company supplies power to large swathes of northern California, and runs power lines connected to hydroelectric power generators in the foothills of the Sierra Nevada mountains. A tower on one of those lines, constructed in the 1920s in the north fork of the Feather River canyon and well past its projected lifespan, is implicated in the Camp fire.

A vehicle rests in front of a home leveled by the Camp fire in Paradise, California. Photograph: Noah Berger/AP

At about 6.15am on 8 November, there was an outage on the line, and PG&E employees and contractors reported seeing a patch of flames below it. Within a matter of hours, the flames had leaped from the canyon and raced several miles to the towns of Paradise and Magalia.

PG&E infrastructure had earlier been fingered for the Butte fire in 2015, which left two people dead,and a 2010 pipeline explosion in the town of San Bruno that killed eight people.

Critics say that because PG&E is an investor-owned company, it is incentivized to direct profits to shareholders rather than to safety measures. PG&E counters that its customers’ wellbeing is its top priority.

Yet investigators have consistently found cause for concern, and a 2013 report to the California public utilities commission stated that “several aspects of the PG&E distribution system present significant safety issues”.

In Paradise, the pace of rebuilding is slow. According to the mayor, news about the fire’s ignition will seem secondary to immediate, more material concerns.

“I haven’t heard anybody talk about that in months,” Jones said. “People are more focused on rebuilding, getting their lots cleared, getting their building permit, finding a place to live in the meantime.”

But, Jones added, she was hopeful the findings may be helpful in negotiations over the town’s lawsuit against PG&E. And it may spur progress in many of the other lawsuits filed by Paradisians who lost relatives or homes.