Two people were brought into a sheriff's station Monday for questioning and released, according to James Crowell, assistant special agent in charge with the Bureau of Alcohol, Tobacco, Firearms and Explosives.
Riverside County Sheriff Bob Doyle cautioned investigators would be interviewing a number of people in the case. No arrests have been made and the reward for information topped $500,000.
"We're trying to work through the leads that we have, and going through the process," Doyle said in a telephone interview.
Before firefighters contained it Monday evening, the fire scorched 40,200 acres — or about 63 square miles — and destroyed 34 homes. It erupted Thursday as fierce Santa Ana winds blew through the region.
Authorities said the fire was deliberately set at the base of a slope in Cabazon, west of Palm Springs. Residents said they saw two young men leaving the area where the fire began.
Several hours into the blaze, a U.S. Forest Service engine crew was overrun by flames while protecting a home in the San Jacinto Mountains. Killed were Mark Loutzenhiser, 43, of Idyllwild; Jason McKay, 27, of Apple Valley; Jess McLean, 27, of Beaumont; and Daniel Hoover-Najera, 20, of San Jacinto.
The lone survivor of the fire crew, Pablo Cerda, 23, remained in critical condition at Arrowhead Regional Medical Center.
Cerda underwent surgery Friday to remove damaged skin.
About 50 of Cerda's relatives gathered at the hospital and prayed for him. "They want everyone to know that Pablo's dream was to help people, and on Thursday morning, that's just what he was doing — protecting and serving," said Eddie Cortez, a family spokesman.
"Everyday, it's just wait and see," said Tomas Patlan, a U.S. Forest Service spokesman. "They're trying to make sure he's breathing on his own, make sure there's no infections. Those are goals, one battle at a time."
Six other firefighters suffered minor injuries.
On Monday, sheriffs deputiesfrom a house in Cabazon around 1 p.m., according to neighbor Robert Dunham, 70, who lives three doors down from the residence a quarter-mile from where the fire started.
The FBI and the ATF donated $25,000 apiece toward the reward pool, bringing the total to $550,000, ATF spokeswoman Susan Raichel said.
"At this time there are no suspects," she said. "We have over 250 leads and tips. Increasing the reward makes people really go back and think over what they've seen and heard. All it takes is one phone call to make or break an investigation."