Fingerprints are blurred by soot. The arsonist flees before passersby even notice the flames. The blaze burns so quickly that pinpointing the exact spot where it started is nearly impossible.
For arson investigators, gathering evidence and identifying a suspect is difficult. For prosecutors, piecing together the puzzle to file charges and win a conviction is even harder.
As massive brush fires continue to ravage Southern California, teams of investigators from the U.S. Forest Service, the California Department of Forestry and local agencies are already working to determine the causes and track down the arsonists.
Using infrared goggles, digital cameras and fine-hair brushes, they are photographing shoe prints and vehicle tracks, interviewing witnesses and digging through ashes in search of ignition devices.
At least four of the major fires in the region are considered arson or suspected arson, authorities said. No arrests have been made, but a possible suspect has been identified in one of the Ventura County blazes and a hunter has been cited for allegedly igniting the Cedar fire in San Diego.
In San Bernardino County, witnesses told investigators about a van that was seen leaving the area where the Old fire began and about a suspicious person on a motorcycle near where flames were first spotted in the Grand Prix fire.
Despite the meticulous work of investigators, many arson fires are never solved. There are arrests in only about 10% of arson fires nationally, said Jim Thornton, a Los Angeles fire investigator who has testified in more than 100 criminal cases. Even fewer cases are actually taken to court.
For example, no arson charges were ever filed in one of the worst wildfires in Southern California history -- the 1993 Malibu fire, which killed three people and caused $375 million in damage. The Los Angeles County district attorney's office said it did not have enough evidence to prosecute two firefighters who had been named as suspects.
The next year, charges were dismissed in the catastrophic Laguna Beach firestorm that destroyed 441 homes and caused $528 million in damage.
The Orange County district attorney's office filed charges but then was forced to drop them after admitting that the suspect had been in a Mexican prison at the time when, according to his confession, he was supposed to have set the fire in 1993.
Contributing to the problem is the scarcity of witnesses and forensic evidence. What does exist -- ignition devices, magazines, matches -- may have burned in the fire.
"You don't have an eyewitness saying, 'I saw him put a match to that bush,' " said Sgt. Julio Salcido of the Los Angeles County Sheriff's Department arson unit.
Arsonists usually work alone, said Jean Daly, the head arson prosecutor for the Los Angeles County district attorney's office. They also plan their actions, looking for thick brush and lightly traveled areas.
"Arson is the crime of a coward," Daly said. "They hide behind trees and they hide in the dark, so nobody can see what they do."
Unless there is a financial motive, such as insurance fraud, it's difficult to find a suspect, said San Francisco attorney Walter F. Brown Jr., a former federal prosecutor. As a result, it's often easier to identify suspects in structural arsons than in brush fires.
But anyone who may have been in the area at the time a fire started can be crucial, helping investigators determine where a fire began or who might have been responsible.
An investigation typically begins by attempting to establish the point of origin, in an area where dozens of acres of earth can be scorched within minutes. Investigators scour charred ground -- often on their hands and knees -- in search of clues.
"You first look for burn indicators on twigs and rocks," said Cheryl Johnson, a U.S. Forest Service wild land fire investigator. "Fire leaves a footprint. It starts cooler and goes out hot, leaving heavier scarring as it progresses."
In determining whether the fire was arson, investigators look for crude ignition devices, such as a matchbook left to burn with a rock placed on top or a can with an incendiary concoction of brake fluid, aluminum foil and chlorine inside. Dogs sniff for kerosene or lighter fluid, and investigators collect dirt clumps in plastic bags.
DNA evidence can be obtained from burned-out cigarette butts at the scene, and fingerprints can be lifted from discarded beer bottles or soda cans.
"Sometimes you get lucky, other times you don't find much at all," Johnson said.
Even after an arrest is made, prosecutors still have to put the case together. To get a conviction, prosecutor Daly said videotapes and confessions aren't necessary.
But the prosecutor has to connect the suspect to the fire, through his statements or any tracks he may have left behind. The prosecutor also has to prove that the arsonist intentionally started the fire.