SAN FRANCISCO—Pacific Gas & Electric Corp. power lines sparked a Northern California blaze that killed 85 people last year, making it the deadliest U.S. wildfire in a century, state fire officials said Wednesday.

Cal Fire said transmission lines owned and operated by the San Francisco-based utility started the Nov. 8 fire that nearly destroyed the town of Paradise in the Sierra Nevada foothills.

The fire wiped out nearly 15,000 homes. Many of those killed were elderly or disabled. The oldest was 99.

“Investigators determined there were violations of law,” Cal Fire deputy director Mike Mohler said. He said he hadn’t read the report and didn’t know the nature of the violations.

Cal Fire did not release its full investigative report, saying it had been forwarded to the Butte County district attorney’s office, which is considering criminal charges against the utility.

The investigation also identified a second nearby ignition site involving PG&E’s electrical distribution lines that had come into contact with vegetation. The second fire was quickly consumed by the initial fire.

The disclosures came on the same day the utility’s new chief executive was testifying before a legislative committee in Sacramento. Bill Johnson told the state Assembly Utilities and Energy Committee he had expected the utility would be blamed for the fire.

“I have made the assumption when I got here that PG&E equipment caused the fire,” he said, noting the utility had said that was probable in recent filings. “It’s a disappointment that this happened. Let’s not do it again.”

Butte County District Attorney Mike Ramsey said in a statement that he is still weighing possible criminal charges against the utility, a decision that could take months. He called Cal Fire’s decision to forward its report to Butte County “strictly symbolic.” because it has been long known that PG&E’s equipment caused the fire.

State fire investigators have determined that PG&E caused 18 wildfires in 2017. They referred 12 for possible criminal prosecution.