The deadly 2025 Eaton fire in the Los Angeles area was caused by equipment belonging to the utility company Southern California Edison, fire officials said in a report released on Tuesday.

Los Angeles county fire officials found that the cause of the fire that killed 19 people and destroyed or damaged more than 9,000 homes and businesses was a tower that was not in service, according to the report.

“After 18 months of thorough review of all evidence, alongside retained electrical and metallurgical experts, the investigation concluded that the cause of the wildfire conflagration was due to the electrical arcing events that took place on the out-of-service Southern California Edison (SCE) tower,” the agency said in a statement.

It took firefighters nearly a month to extinguish the blaze, which scorched 22 sq miles (57 sq km).

Kathleen Dunleavy, a spokesperson for Southern California Edison, said the utility has received the report and is reviewing it.

“We have taken our potential role in the start of this fire seriously from the very beginning,” Dunleavy said. She said SCE previously acknowledged “it was likely our equipment was associated with the ignition of the Eaton fire”.

She said the utility continues to support the community as it recovers.

SoCal Edison has claimed in lawsuits earlier this year that Los Angeles county agencies failed to send timely evacuation warnings to residents in east and west Altadena. Eighteen of the 19 people who died in the fire lived in west Altadena.

The utility also has claimed water agencies, including Pasadena Water and Power, did not provide enough water as the fire spread, leaving firefighters with limited resources. Los Angeles county declined to comment about the latest court filings.

The Los Angeles county arson fire investigation unit jointly conducted the investigation with California department of forestry and fire protection. It found electrical arcing on the utility’s out-of-service tower sparked the dry brush below and that the utility was responsible for maintaining and operating its electrical lines and equipment “in a manner that would minimize the risk of catastrophic wildfire posed by them.”

The blaze was sparked during extreme weather conditions that included high temperatures, low humidity and powerful winds. Two “electrical arcing events” occurred in quick succession, causing an unknown burning material to fall from the tower to the ground below, according to the report.

Within 12 seconds, dry grass and brush was ignited and the fire swiftly developed “into a conflagration engulfing the areas of the San Gabriel Mountains, Altadena, Pasadena, Sierra Madre and La Cañada Flintridge”, the report said. It took more than two weeks to fully contain the wildfire.

The report cites an interview with a Pasadena resident who called 911 on 7 January after spotting flames across the canyon from his home’s rear window. The caller described it “as a 10in x 10in fire at the base of a high-voltage electrical tower”, the report said.

The Eaton fire burned at the same time as the Palisades fire, the most destructive blaze in Los Angeles to date and among the five worst in California’s history. The blaze killed 12 people and destroyed more than 6,800 homes and buildings in Pacific Palisades. The fire ripped through hillside neighborhoods, destroying mansions with spectacular ocean views.

The man accused of sparking the Palisades fire will be tried again this fall after his first federal arson case ended in a mistrial in June. Prosecutors said Jonathan Rinderknecht used a barbecue lighter on 1 January 2025 to spark a blaze that burned undetected deep in root systems before flaring back up 7 January.