BOULDER, Colo. (AP) — Colorado firefighters have boxed in the big fire that destroyed nearly 1,000 homes in their effort to prevent it from spreading — but officials warned Tuesday that gusty winds expected ahead of a snowstorm could cause flareups in the burn zone between Denver and Boulder.

About 200 firefighters were working to douse smoldering spots in damaged buildings and bone dry vegetation that serves as tinder to fan wildfire flames as the gusty winds descend from the Rocky Mountains.

The fire that started last Thursday was finally fully contained Tuesday by firefighting crews from across Colorado; the blaze burned 9.4 square miles in suburban areas and grassland northwest of Denver, said David Boyd, spokesman for an incident management team in charge of the fire’s suppression in Boulder County.

Although the blaze died down in recent days and was no longer considered a threat because of a snowstorm last weekend, firefighters were going door to door looking for smoldering that could cause flareups ahead of winds expected to reach 30 mph, with gusts up to 60 mph, Boyd said.

“Our concern with the strong winds is a lot of destroyed structures have a fragile wall or chimney still standing that could come down,” Boyd said. “It’s a hazard for the public, too. People going back into their homes need to be aware of that instability.”

Whipped by winds reaching 100 mph last week, the inferno destroyed nearly 1,000 homes and other structures and forced tens of thousands of residents to evacuate the rapidly growing suburban area pockmarked by grasslands.

Two people were still missing Tuesday, and crews sifted by hand the locations where they lived, using small tools in their search for any remains.

Federal and state investigators have interviewed dozens of people in their search for the fire’s cause. Results of that investigation — and even a progress report — could take days, if not weeks, Boulder County Sheriff Joe Pelle said Monday.

Pelle said part of the investigation in the area where they think the fire started includes property occupied by members of The Twelve Tribes, a Christian religious community founded by a Tennessee high school teacher in the 1970s that is thought to have 2,000 to 3,000 members worldwide. But Pelle said when asked about it at a Monday news briefing that the group isn’t the only focus of the investigation, which hasn’t yet honed in on a suspected cause.

Twelve Tribes didn’t respond to a voicemail and email sent Monday by The Associated Press to a number and email listed on the group’s website. A man who answered a different phone number affiliated with the group said Tuesday that nobody is authorized to speak for the organization and declined to identify himself.

Experts have said that 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 blaze followed months of drought that included a dry fall and little snow up until this weekend.

The investigation into the fire’s origin is focused on an area near Boulder where a passerby captured video of a burning shed on the day the fire began, Pelle said. Authorities have said that no downed power lines were found in the area.

Known as Marshall Mesa, the area in unincorporated Boulder County lies near the base of the Rocky Mountain foothills and overlooks more heavily populated suburbs that were devastated by the fire. Marshall Mesa is surrounded by tinder-dry public open space and private grasslands.

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.

Louisville police Chief Dave Hayes said authorities were using cadaver dogs to re-check 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.” Hayes told reporters Monday that he lost his home and was wearing a change of clothes he asked someone to buy for him.

Among the homes that were still intact, utility crews went door to door to check if natural gas and electricity could be safely restored.

“What a relief,” uttered Louisville resident Carl Johns as a utility worker turned on a gas valve and went inside Johns’ home of 21 years to make sure appliances were lighting up. He had been living with friends since Thursday, when police drove through the neighborhood and urged everyone by loudspeaker to evacuate.

Some of his neighbors weren’t so lucky. Down the street stood a row of burned homes.

“That just blows me away,” Johns said. “The houses aren’t there, and you can’t recognize your own block.”