(CNN) -- It was the second day of the massive 2002 Hayman wildfire that charred nearly 138,000 acres just outside Denver, Colorado, destroying more than 100 homes and sending 8,000 fleeing for safety.
A California Department of Forestry investigator looks for clues in Orange County on Thursday.
Douglas County Undersheriff Tony Spurlock picked up his phone. Officials from the Colorado Attorney General's Office told him state fire officials needed his help.
They had an arsonist on their hands.
As firefighters battled intense winds to tame the state's worst wildfire in history, Spurlock and a team of investigators narrowed the fire's origin to 10 acres. Watch investigators find clues from soot »
A man who saw a plume of smoke during the first few hours of the blaze pointed investigators in the right direction. Soon, they found a pit constructed with rocks and dry leaves, cutting a path toward open, scorched bush.
In the center of the pit were burned matches.
The evidence was tied to a shocking suspect: U.S. Forest Service worker Terry Barton, who had burned a letter from her estranged husband. She pleaded guilty in 2003 to arson and was sentenced to prison.
Barton was one of the first to call authorities about the fire, said Spurlock.
"She wanted to be some kind of hero," he said. "I don't think she was prepared for the magnitude of her actions -- all the homes that were lost, the pets that died, the land lost."
On Thursday, Orange County, California, investigators said they suspect arson in one of the largest of the fires that have ravaged the state since Sunday. The Santiago Fire has destroyed 26,000 acres. Watch how the fire spread so fast a fire chief said the arsonist must be lucky or knowledgeable »
Spurlock and other investigators discussed how the investigation will likely proceed. First, experts will be brought in to create a criminal profile.
"There are so many kinds of arsonists," said Joe Sesniak, a longtime fire investigator with the International Association of Arson Investigators, which trains arson detectives around the country.
One type of arsonist is a "hero," Sesniak said. An example is John Orr. He was a fire captain and arson investigator with the Glendale Fire Department in Southern California. Orr was convicted of setting three fires in 1987.
The majority of fire-setters are children fascinated by flames, Sesniak said. Some arsonists get sexual satisfaction from setting fires, others want to collect insurance money or are motivated by revenge, he said. So-called eco-terrorists are out to destroy development projects they feel are infringing on natural habitat.
Though profiles vary, a fire investigation is always a tedious, time-consuming job, Sesniak said. "It means getting on your hands and knees with a magnifying glass," he said. A wildfire investigator has to rule out natural causes. Was there lightning in the area? Were there logging operations that might have produced a spark?
Experts said the first task is finding a fire's origin. Wildfires leave clues along the way as they spread. Investigators examine the angle of burns on grass, shrubs and tree trunks to determine the direction and intensity of a fire, in much the same way a highway patrol officer determines the direction a car skidded by studying the skid marks.
Investigators examine the way burned grass is leaning and where soot is thickest to help determine where the fire is heading. Because heat rises, investigators configure the depth and height of a burn on, say, a tree, to also help determine the direction of a blaze.
Often joined by accelerant-sniffing dogs, investigators use handheld magnifiers and magnets to detect metallic residue from an accelerant a sophisticated arsonist might assume is tough to track. It's common for arsonists to leave behind "delay devices," typically a lit cigarette tied to a matchbook, Sesniak said. Watch an investigator say the Orange County arsonist must be crazy »
Evidence undergoes forensic testing. In the case of the Colorado wildfire, the same kind of matches were found in Barton's truck as were found at the scene, Spurlock said. A piece of paper found at the site also was linked to her.
But investigators said old-fashioned gumshoe detective work also is essential to catching an arsonist.
"You may have to canvass an entire neighborhood, asking people if they saw a vehicle or a person who didn't fit the area," said Sesniak. "Ultimately, if you decide to charge somebody, you have to make sure the conclusions of the investigation are scientifically sound."
The experts who spoke to CNN said it is difficult to get a conviction in arson cases.
"For us to arrest somebody, we have to be beyond a reasonable doubt," said Lt. Joseph Schwartz of the Florida Fire Marshal's Office.
"Fortunately, there's not a lot of smart arsonists," said Schwartz, who has investigated fires in which people have taped hairdryers and left them running or, in a rage, poured gasoline on structures in plain sight and lit a match.
"There's still a mentality out there that if you burn it, it's gone, there's no evidence," said Schwartz. "There's almost always going to be evidence. It just takes a lot of work and determination to find it." E-mail to a friend