Updated

There have been more than 500 tips, dozens of cars stopped, a handful of men questioned, at least one confession and endless rumors, but authorities say they still haven't arrested anyone who sparked one of the Southern California wildfires.

There could be lots of suspects. Arson is blamed for at least three of the seven wildfires still burning in the region.

On Thursday, the San Bernardino County (search) sheriff's office fleshed out a description of a suspect — a thin, blond man in his 20s who witnesses say stepped out of a gray van last Saturday, dropped something into the brush causing a fire, then climbed back into the van before it sped away. The wildfire has grown to about 50,000 acres, killing four people and destroying 850 homes.

A police sketch of the van's driver, a dark-haired man in his 20s, has appeared on newspaper front pages and television news broadcasts all week.

"We've got a lot of good leads. We're working hard on this," said sheriff's spokeswoman Cindy Beavers.

Dozens of federal, state and local arson detectives have been working around the clock, talking to witnesses at evacuation centers, studying burn patterns where the fires began, and calling for public help.

Forest Service agent Jerry Moore said a man had confessed to starting a Ventura County fire that burned three homes and 68,000 acres, but the case remained under investigation.

"Anybody can come in and say 'I did it,"' Moore said.

San Diego County authorities, meanwhile, said they are positive a wildfire that has so far killed 14 people, including a firefighter, and burned nearly 1,500 homes was sparked by a lost deer hunter who set a signal blaze.

He was given a misdemeanor citation. Arsonists could face federal or state charges, including aggravated arson, which in California carries a sentence of 10 years to life in prison. They could even face murder charges.

Investigators had no motive for the arsons. In the past, people have set "vanity fires" so they can point them out and appear to be heroes, said Daniel Frias, a fire investigator with the state Department of Forestry and Fire Protection. Others have tried to torch houses out of revenge.

Various agencies are receiving as many as 100 tips a day from as far north as San Francisco, but finding wildfire arsonists can be difficult, Frias said, because they can set time-delay devices or wait until the coast is clear.

"Usually when we get a good lead, it's because a witness just happened to be driving by," he said.