BOULDER — Embers buried for six days on a residential property reignited and together with sparks from an “unmoored” Xcel Energy power line started the 2021 Marshall fire in Boulder County, the sheriff said Thursday morning.

A residential fire on Dec. 24 to burn scrap wood and tree branches resurfaced because of the winds on Dec. 30, Boulder County Sheriff Curtis Johnson said. The sheriff said the fire was put out “responsibly” on Dec. 24 when it was buried. But around 11 a.m. on Dec. 30, high winds, pushing 100 mph, resurfaced embers and started a shed on fire at 5325 Eldorado Springs Road.

Johnson said a second fire was started that day by Xcel power lines and also quickly spread. At some point, the two fires combined.

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The sheriff, who lost his house in the fire, said the underground coal fires also cannot be ruled out.

The district attorney’s office determined there was “insufficient or no evidence of a crime” and no reason to file charges, Boulder County District Attorney Michael Dougherty said.

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“If we were to tell you today that we were filing charges it would be wrong and unethical,” he said. “We can only file charges if there’s evidence of a crime being committed.”

He added there is no evidence of negligence or recklessness by Xcel. Rather, high wind caused a power line to disconnect and contact other lines, leading to electrical arcing and hot particles showering into dry grass. 

There were no known problems with the power line prior to the fire, Dougherty said. “This is a different discussion and a different decision if that wire was worn or shoddy or they had maintenance issues in the past. There was no such record of that, no indication of that.”

The announcement comes nearly 18 months after the fire exploded in late December 2021 and raced across 6,000 acres, as gale-force winds pushed embers across parched grassland into subdivisions bordering open space. Two people died in the fire, and more than 1,000 homes and businesses were destroyed in Louisville, Superior and unincorporated Boulder County. 

In addressing the disastrous toll of the fire, Curtis choked up and thanked the community for its patience as the investigation played out. 

“I know personally the last 18 months have been hard and not having answers creates stress and challenges that we don’t need,” he said in a quavering voice. “And I hope that now we can focus on rebuilding our lives and getting back to our homes and our community.”

The Boulder County Sheriff’s Office said the fire likely started near Marshall Road and Colorado 93, but federal agencies aided in its investigation to try to pinpoint the cause of the fire. 

Evidence included hundreds of  body camera recordings and photos that were captured by first responders during the initial response of the fire, along with 49 physical items and 137 pieces of digital evidence, such as drone footage and video recording by witnesses, the sheriff’s office said. 

The fire also raised questions about Boulder’s emergency notification system, which is designed to send fire warnings and evacuation alerts to people who signed up to receive them. Records obtained by The Colorado Sun showed that the first phone alert was sent 42 minutes after the fire started and only to 215 people. By then, at least one structure had burned and the fire was well on its way toward consuming more than 1,000 homes and businesses. 

Since the fire, the sheriff’s office said it has improved the county-wide notification system and now uses Amber Alert-style warnings that can be sent directly to the cellphones of people who may be in danger based on their GPS coordinates. The county acquired the technology prior to the Marshall fire but had not finished setting it up. 

Updates have also been made to the county’s other phone alert program, Everbridge, which sends alerts via landlines, cellphones, emails and text messages to those who register, the sheriff’s office said last month.

Boulder County strengthened its ordinances last year to provide specific guidelines on how to fully extinguish fires, Johnson said.