(CBS News) The worst wildfire in Colorado history could lead to a criminal investigation.
Officials have ruled out a "natural" origin for the Black Forest fire, near Colorado Springs, but finding the cause may be even harder than putting it out. Investigators suspect the Black Forest fire that destroyed more than 500 homes -- the worst in Colorado history -- was caused by humans.
The wildfire started in the west and roared to the east and then north, growing to more than 22 square miles. Now, with help with Bureau of Alcohol, Tobacco, Firearms and Explosives arson investigators, the hunt is on to track the fire back to its first minutes.
CBS News' Barry Petersen said, "How do you get down to a cigarette that somebody threw away or a campfire that didn't go out?"
Rich Harvey, the Black Forest fire's incident commander, said, "Well, 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."
But it doesn't always work. A year after a fire 12 miles away in Waldo Canyon burned 350 homes, investigators still don't know if someone set it deliberately.
Veteran arson investigator Doug Allen said, "There are fires that we look at that we just can't find the cause."
Allen has more than three decades of experience, helping in the conviction of a serial arsonist who was given the death penalty for starting a California blaze in 2006 that killed five firefighters. He says it was solved using painstaking detective work, with evidence from the forest and the suspect's home.
Allen said, "All of these bits and pieces come together as a mosaic -- it's like putting together a crossword puzzle -- and once all these pieces fit, you've solved the crime and the whodunit."
Allen says if the Colorado fires were arson-related, it's vital to find the person responsible soon. He said, "This won't be the person's last fire -- they'll continue to set fires."
Watch Barry Petersen's full report in the video above.