LOS ANGELES – The western flank of the deadly wildfire north of Los Angeles was under control Saturday, sparing foothill communities further threat as it burned east into a large wilderness area.

Investigators, meanwhile, were trying to determine who ignited the blaze that killed two firefighters, destroyed at least 76 homes and burned nearly 242 square miles of the Angeles National Forest.

The fire’s origin near Angeles Crest Highway remained cordoned off as authorities sought more clues in the case, but they were hesitant to release any findings to the media.

“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.