"Arsonists are not stupid. They can read," said U.S. Forest Service Cmdr. Rita Wears, who supervises federal agents investigating the fire. "I have to be very careful."
Los Angeles County firefighters Tedmund Hall and Arnaldo Quinones were killed Aug. 30 while seeking an escape route for their inmate fire crew after flames overran their camp on Mount Gleason.
Sheriff's detectives opened a homicide investigation after the fire was ruled arson earlier this week, and Gov. Arnold Schwarzenegger has offered $100,000 for information leading to the arrest and conviction of the culprit.
The fire, one of the largest in Southern California history, was 49 percent contained Saturday night after crews built protective lines on the northwestern flank near Santa Clarita, said incident commander Mike Dietrich.
"We're making tremendous progress," Dietrich said, "but we have not turned the corner on this fire. I keep seeing that it's out there, but we have not turned the corner yet."
Dietrich said about 400 firefighters assigned to protect structures had been dismissed because of the reduced threat. About 4,800 firefighters remained.
Despite the gains, two new flare-ups presented challenges. The fire jumped a closed section of the closed Angeles Crest Highway and burned about 500 new acres in the Pleasant View Ridge Wilderness Area, Dietrich said. Flames were within about five miles of the community of Juniper Hills and firefighters will make the area their primary focus into the night.
Dietrich said crews also were fending off new fire activity on the southeastern end of the fire and trying to keep the blaze from burning into Santa Anita Canyon and Chantry Flats north of Arcadia and Monrovia.
And firefighters were trying to slow the eastern movement into the San Gabriel Wilderness and secure the southeastern flank north of Arcadia, Monrovia and other foothill communities.
No homes were immediately threatened in either area, said. The weekend weather forecast called for cooler temperatures and slightly higher humidity that could help firefighters further surround the blaze.
Mount Wilson - which holds a historic observatory and at least 20 television transmission towers, radio and cell phone antennas - appeared well-protected after flames came dangerously close earlier this week.
However, "we've still got the potential all around us," said Quinn MacLeod, the U.S. Forest Service's supervisor for Mount Wilson.
MacLeod ordered crews to wrap communication towers with protective material and clear areas of concern on Mount Wilson's western slope where smoke was rising from various hot spots. He pointed to two 5,000-gallon trucks filled with retardant. "Those are like our ace in the hole," he said.
Fire agencies have spent $43.5 million to fight the blaze, which started Aug. 26 and has scorched 154,655 acres.
MacLeod said monetary costs are irrelevant, considering the fire has already killed firefighters.
"My whole philosophy is, one billion dollars? I'm OK with that," he said. "If it's lost and nobody gets hurt, I'm OK with that."
At least a dozen investigators were working to analyze clues found at a charred hillside near Angeles Crest Highway, including incendiary material reported to have been found there. Officials said the fire was arson but were still investigating who started it and how.
"We are in the early stages, just beginning to put things together," said sheriff's Lt. Liam Gallagher, who is heading the homicide investigation. "Firefighters losing their lives in the line of duty is an added incentive, but we work every case to the fullest."
Near a large shade tree where crews get their daily briefings, firefighters set up a makeshift memorial for Capt. Hall and Specialist Quinones. The fallen firefighters helped save about 60 members of their inmate crew from approaching flames when they set a backfire that allowed the group to get to safety. The pair died when their truck plunged 800 feet off a steep mountain road.
County and state corrections officials are considering rebuilding the camp and naming it after the firefighters, though they were not sure if the same site would be chosen.
"That would be hallowed ground," said state Corrections Department Lt. David Foote, the camp commander at Mount Gleason and friend of the victims.
"We're trying to come up with something positive out of this tragedy."
Foote said he has struggled to cope with the deaths, but is finding some comfort in remembering the good times, such as a Christmas party last year at Hall's home in which the captain dressed up like Santa Claus and put Foote's daughter on his lap. "We were family," he said.
Foote compared the fire investigation to an arson three years ago in which five federal firefighters died battling a blaze 90 miles east of Los Angeles. Raymond Oyler was convicted of five counts of murder for starting that blaze and was sentenced to death.
Foote wants the culprit in the latest fire to face the same fate.
"I hope justice prevails," he said.
Associated Press writers Allen G. Breed and Raquel Maria Dillon in Los Angeles contributed to this report.