After two deaths and at least 500 lost homes, local officials are calling Colorado’s Black Forest wildfire not just the most destructive fire in state history, but also the site of a criminal investigation.

The return of residents to their homes is being tightly controlled as a result, The Denver Post reports, to preserve as much evidence as possible.

"This is a crime scene until proven otherwise," El Pasco County Sheriff Terry Maketa said at a press conference Monday. "I won't compromise that by letting people in too soon."

Mr. Maketa clarified that he did not know if any crimes were committed, but authorities would treat it as if it were a crime scene until they could make a conclusive determination. Local authorities suspect the fire has a human cause, media reports say.

Five hundred two homes have been lost in the 22-square-mile fire near Colorado Springs, which is 75 percent contained, according to the Associated Press, which cited sheriff's officials Monday. While evacuations reached a peak of nearly 40,000 over the weekend, the mandatory evacuation area dropped to include 4,100 people Monday, CNN reports.

Authorities are investigating two issues, according to media reports: the start of the fire and the deaths of two people as they were apparently trying to evacuate their house. Their deaths have been classified as homicides, according to The Denver Post, until further information is known.

Maketa told the Los Angeles Times that the possible homicides were the reason he had called the site a criminal investigation.

Federal investigators from the Bureau of Alcohol, Tobacco, Firearms and Explosives have been called in, along with state authorities, CNN says.

As to the cause of the fire, investigators are zeroing in on the fire’s “point of origin,” according to Maketa. Ideally, once that origin is discovered, clues about the fire's start, such as matches or a cigarette butt, can be found, says Rich Harvey, Black Forest fire incident commander.

"You kind of look at the burn patterns and work your way backwards. Kind of tracking the footprints the fire left as it moved away from the point of origin back to the point of origin. Once you get to the point of origin, you look for clues: cigarette butts, footprints, tire tracks," he told CBS News.

Determining the origin of wildfires is notoriously tricky. The cause of the state’s second-most destructive wildfire, the Waldo Canyon fire, which burned nearly a year ago, still hasn’t been determined, the Associated Press reports. Wind, other weather, tire marks, and first-responder tracks can easily cover traces of a fire’s cause.

But criminal cases have resulted from wildfire investigations, especially in the past five years. In 2009, Raymond Lee Oyler was convicted of murder and sentenced to death for arson charges in a string of 2006 California wildfires, including the Esperanza fire that killed five firefighters.

In January of this year, a second arsonist, Rickie Lee Fowler, was sentenced to death for a 2003 fire in California's San Bernardino Mountains, which burned 91,000 acres and about 1,000 houses and was blamed for the deaths of five people.

The past 60 years have seen an evolution of much stricter penalties for arsonists, writes John N. Maclean, the author of several books on wildfires, in a High Country News article.

“The conviction of Raymond Oyler for murder would have been unthinkable a century or even a few decades ago,” he writes, referencing a 1953 wildfire where the arsonist, who admitted starting a fire to get a job on the fire crew, was charged with two counts of willful burning and spent just three years in prison. That fire killed 15 firefighters.

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In the years since, arson sentences have gotten progressively stronger, he writes. Terry Lynn Barton, a seasonal Forest Service worker, served six years in prison for starting Colorado’s Hayman fire, which burned 138,000 acres and 133 houses in 2002. And Mr. Oyler became the first arsonist sentenced to death.

“The Oyler case stands as a warning to every would-be fire starter: Tolerance for the torch has gone the way of the Old West,” Mr. Maclean writes.