BOULDER, Colo. (AP) — Investigators seeking the cause of the Colorado wildfire that destroyed nearly 1,000 buildings have narrowed their search to an area near Boulder, but it could be days or weeks before details are released, the sheriff said Monday.

The search is focused on an area where a passerby captured video of a burning shed on the day the fire began, Boulder County Sheriff Joe Pelle told a news briefing. He said dozens of people have been interviewed thus far.

Experts from the FBI, the Bureau of Alcohol, Tobacco, Firearms and Explosives, and the U.S. Forest Service were participating in the investigation, Pelle said.

The sheriff declined to offer many more details Monday, a day after saying that the fire “originated somewhere” in the neighborhood with the burning shed.

Declaring that ”the stakes are huge,” Pelle said he would not comment on the probe until he was ready “to announce some progress — perhaps that may be a week, perhaps that may be a month.”

Getting it right, he said, was “more important than the urge for speed that a lot of folks are feeling right now.”

Experts say the winter fire was rare but that similar events will become more common as climate change warms the planet and suburbs grow in fire-prone areas. The inferno broke out unusually late in the year following months of drought that included a dry fall and a winter with hardly any snow so far.

No downed power lines were found in the area being investigated, according to the county’s Office of Emergency Management.

Meanwhile, teams continued searching Monday for two people who were still missing, and survivors sorted through the charred remnants of their homes to find whatever was left.

The Boulder County area known as Marshall Mesa is near the base of the Rocky Mountain foothills and overlooks the more heavily populated suburbs to the east that were devastated by the fast-moving fire, which was whipped up by furious winds blowing from the foothills. The area is surrounded by tinder-dry public open space and private grasslands.

Over the weekend, authorities executed a search warrant, but the sheriff declined to elaborate and did not comment on whether he thought the fire was arson.

A sheriff’s official who spoke on condition of anonymity confirmed that several properties were under investigation, including one in the Marshall Mesa area, about 2 miles west of the hard-hit town of Superior. A National Guard Humvee blocked access to the neighborhood Monday.

“The first thing you have to do is kind of get a rough idea of where this this fire starts,” Robert Rowe, a fire investigator and code consultant, said on NewsNation Prime on Monday.

Rowe said investigators can do this through aerial operations, which allow them to look down on the fire.

“Then, you just start talking to people in the area, you start talking to first responders, what they’re seeing and the early stages of the fire,” Rowe said. “Then, you basically kind of develop an area of origin. And once you get the area of origin established, then you have to process the fire scene.”

See Rowe’s interview in the player below.

In the search for the missing, crews were looking for a woman in the town of Superior and a man from the nearby community of Marshall. Pelle said the crews were sifting debris by hand and using small tools.

Louisville police Chief Dave Hayes said authorities used cadaver dogs to recheck destroyed properties as a precaution. He said no one was reported missing in the heavily damaged city, but that “doesn’t mean we won’t find something.”

Gov. Jared Polis told the briefing that it was “remarkable that a fire of this speed and size” resulted in only two people missing. Tens of thousands of people evacuated Thursday, and Polis emphasized the importance of heeding evacuation orders.

“When you get a pre-evac or evacuation notice, hop to it. The residents did, and most of them are with us today,” he said.

While homes that burned to the foundations were still smoldering in some places, the blaze was no longer considered an immediate threat — especially with frigid temperatures and a blanket of snow that fell Saturday.

Most of the 991 buildings destroyed by the fire were homes. But the blaze also burned through eight businesses at a shopping center in Louisville, including a nail salon and a Subway restaurant. In neighboring Superior, 12 businesses were damaged, including a Target, a Chuck E. Cheese pizzeria, a Tesla car dealership, a hotel and the town hall.

The two towns are about 20 miles northwest of Denver and have a combined population of 34,000.

The Boulder Valley School District, which serves the wildfire area, planned to resume classes as scheduled Wednesday and to provide counseling services for students and staff affected by the flames. The University of Colorado in Boulder delayed in-person classes to Jan. 24, with remote learning starting Jan. 10.

The flames stopped about 100 yards from Susan Hill’s property in Louisville. She slept Saturday night in her home using a space heater and hot water bottles to keep warm because her natural gas service was still off.

She choked up as she remembered seeing the sky change color and nervously fleeing with her college-age son and the dog, cat and a fire box with birth certificates and other documents.

“I don’t even know how to describe it,” she said. “It’s so sad. It’s so awful. It’s just devastating.”

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