LOS ANGELES — President Bush toured Southern California on Thursday as investigators got down to the work of determining how one sunny fall day last weekend exploded into blazes now in their fifth day.
Recovery crews, moving from house to house in towns where the fires have passed, found the bodies of two people in the shell of a home near Poway, northeast of San Diego. And in the early evening, San Diego officials said, Border Patrol agents found the burned bodies of four people who may have been killed after crossing the Mexican border.
They were the first confirmed fatalities since Sunday, when a man was killed in Protrero, near the Mexican border.
Bush, joined by Gov. Arnold Schwarzenegger, also a Republican, visited the charred remains of neighborhoods, met distraught residents and exhausted fire crews, and viewed fires that continue to burn throughout the region. By Thursday, the fires had destroyed 1,800 homes, injured 57 people and burned more than 487,000 acres.
The president praised Schwarzenegger's handling of the country's biggest natural disaster since Hurricane Katrina two years ago.
"It makes a big difference when you have someone in the Statehouse willing to take the lead," Bush said at a news conference. He also assured California residents that "we're not going to forget you in Washington, D.C."
The president earlier declared seven counties a major disaster area, making residents eligible for federal assistance tohelp them rebuild.
"It's a sad situation out there in Southern California," Bush said Thursday, before leaving for California.
With most of the fires no longer posing a significant threat, fire officials were stepping up efforts to determine how much of the blame for the devastation fell on nature and how much on a criminal element.
In Orange County, where the authorities have already determined a large fire north of Mission Viejo was intentionally set, investigators have begun to interview people about possible suspects, closed canyon roads Thursday and sifted the rubble in search of clues.
The fire there, which is still burning, has consumed 20,000 acres and nine houses. On Wednesday, FBI agents descended on Santiago Canyon Road near Irvine to gather evidence, which was sent to a lab to be analyzed.
"We desperately want to catch the person or persons that did this," said Chip Prather, the Orange County Fire Authority Chief at a news conference in Irvine. The evidence at the scene, which Prather would not discuss further, suggested arson, he said.
A separate fire, to the east in Riverside County, has also been tagged by investigators as arson. At least two people, in San Bernardino and Los Angeles counties, have been arrested on suspicion of arson.
The scale and ferocity of the fires almost certainly stemmed from a trajectory familiar to firefighters, fire investigation experts said.
Fires created through humanerror, lightning or a downed power line typically create large embers that can fly as far as a mile through the powerful Santa Ana winds, setting off new blazes. Early indications point to downed power lines as the culprit in a fire in Malibu and possibly two others.
Arsonists, animated by the flames, begin their pattern of copying them, investigators said, aided by wind, miles of droughtcreated tinder and the steep hills that are prevalent throughout thestate, which make for far better fire-spreading conditions than flatlands.
"It's not by accident that you get 17 or 18 fires going at the same time," said Harold Schaitberger, general president of the International Association of Firefighters, referring to the convergence of natural and accidental factors. "There is no question you then get serial artist copycats out to create the next and larger event."
Last year, arson and murder charges were filed against a 36-year-old man in connection with a wildfire that killed five Forest Service firefighters 90 miles east of Los Angeles. The authorities said they were investigating whether the suspect in that fire was involved with scores of other fires in the region over a number of years.
In 2003, arson was behindsome of 15 fires that roared across six California counties, killing 22 people. In 1993, four people were killed in roughly 20 fires, half of which were found to stem from arson. Investigators are tipped to possible arson when they discover multiple points of origin in a fire - as was the case in the fire now burning in Orange County, according to the fire chief - and other physical evidence.
"Arsonists are fascinated with fires," said Charles P. Ewing, a forensic psychologist and law professor at the State University of New York in Buffalo. "So they are likely the ones following the fires very closely. Then, it's not uncommon for arsonists to engage in copycat activity or to piggyback on a naturally occurring fire."
Arson experts said that while youthful offenders, who tend to set roughly 50 percent of intentional fires, often are curious about fire but do not intend to cause cataclysmic harm, adults' motivations are more complex. Sometimes, Ewing said, "arsonists actually derive sexual pleasure from committing the act," while others are seeking attention and may at times participate in extinguishing the very fires they light.
Two other features of California, its border with Mexico and proclivity of its residents to live along remote canyons and hilltops, contribute to the excessive fire danger.
Illegal aliens who have crossed the border where some of the fiercest fires have raged this week often start camp fires that get out of control, Schaitberger said. And fire travels faster and with more vigor uphill, making those pathways extremely flammable.
Winds, high temperatures and extreme drought contributed to the severity of the current fires. While firefighters had the upper hand on the majority of the fires by Thursday, the fire in OrangeCounty, which flared up late Wednesday night, and one burning near Lake Arrowhead were the biggest challenges. In San Diego County, more than 800 homes remained threatened.
Elsewhere around Southern California, residents began to regroup, returning to homes that had been thankfully spared, or taking in the heartbreaking specter of what used to be. In the San Diego football stadium, the main way station for evacuees, officials estimated that fewer than 1,000 people remained.
San Diego Mayor Jerry Sanders said Qualcomm Stadium, which had housed as many as 10,000 people, would be closed at noon today.
Information for this article was contributed by Jennifer Steinhauer, Randal C. Archibold, Will Carless and Ana Facio Contreras of The New York Times and Allison Hoffman, Elliot Spagat, Martha Mendoza, Scott Lindlaw, Jacob Adelman, Thomas Watkins, Jeremiah Marquez, Gillian Flaccus and Chelsea J. Carter of The Associated Press.
Front Section, Pages 1, 12 on 10/26/2007