Firefighters and law enforcement officials line up Friday at the Station fire command center to salute a procession for Los Angeles County Fire Capt. Tedmund Hall, who died along with firefighter Arnaldo Quinones on Aug. 30 when their truck plunged down a hillside in Los Angeles.

Los Angeles ? Investigators worked around-the-clock Friday as they sought to build a murder case stemming from a huge wildfire that claimed the lives of two firefighters. California’s governor offered a $100,000 reward in the arson case.

Authorities blocked access to the crime scene, a scorched area of scrub and trees off the side of the Angeles Crest Highway, as they analyzed clues including incendiary material reported to have been found there. Authorities say the fire was arson, but are still trying to find a culprit and understand how it was set.

“We are going to find out what we can and present it to the D.A.,” said Los Angeles County sheriff’s Lt. Liam Gallagher, who is heading the homicide probe and whose investigators worked through the night into Friday. “We are considering it a murder investigation.”

Gallagher said as many as 14 investigators would be on hand to help with the probe over the weekend.

“We are in the early stages, just beginning to put things together,” he said. “Firefighters losing their lives in the line of duty is an added incentive, but we work every case to the fullest.”

Gov. Arnold Schwarzenegger offered a $100,000 reward for information leading to the arrest and conviction of whoever set the blaze. The figure is the maximum the chief executive can offer under state law.

Also Friday, authorities said that several firefighters were exposed to cyanide gas in two separate incidents as they were mopping up hot spots near the small city of Acton on the northern edge of the massive blaze.

Deputy Incident Commander Carlton Joseph said four firefighters developed respiratory problems on Tuesday and one suffered respiratory arrest and was still hospitalized on Friday.

Joseph said that on Thursday, six firefighters were digging at a patch of smoke near the first incident when they smelled a sweet odor, like plastic burning, and were briefly hospitalized with respiratory problems.

He said a hazardous materials team investigated and cordoned off the area. He said they found no evidence of dumping and believe the cyanide possibly came from old mining operations.

Arson investigators have plenty of experience to draw upon as they try to figure out who ignited a fire that torched more than 240 square miles of the Angeles National Forest on the edge of Los Angeles and burned 76 homes. The cost of fighting the fire was estimated at $37 million so far.

Most wildfires are caused by human activity, and government statistics show that people were faulted for 5,208 wildfires in Southern California in 2008, the highest number since at least 2001. Between 2006 and 2008, Southern California was the only region of the country to see a significant jump in the number of wildfires blamed on people.

Firefighters paused in their battle against the fire Friday to pay their respects to two fallen comrades whose deaths have triggered the investigation.

Hundreds of weary firefighters who have slogged on the front lines for the past 11 days took off their caps and helmets and bowed their heads at a tribute for Capt. Tedmund Hall and Spc. Arnaldo Quinones, held before dawn at the command center in the foothills near the flames.

The men helped save about 60 members of an inmate fire crew Sunday as flames approached their camp by setting a backfire that allowed the group to get to safety, said Los Angeles County Fire Capt. Glenn Goulet. The pair died when their truck plunged 800 feet down a steep mountain road.

The blaze was 42 percent surrounded Friday, authorities said.