The key to identifying the cause of the still-raging Palisades Fire lies on a brush-covered hilltop where the blaze broke out just after 10:30 a.m. on Tuesday.

Fire investigators are still working to determine what sparked the inferno, but experts say it’s easy to rule out one common cause of wildfires: lightning. The region was free of stormy weather this week. The area near the Temescal Ridge Trail also appears to be free of power lines or transformers, which rules out another potential cause.

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That leaves the source of most wildfires: people. But was it a result of arson? Four experts interviewed by NBC News said it was a possibility, but they thought the fires were more likely not set on purpose.

“This is what we call inaccessible, rugged terrain,” said Rick Crawford, former battalion chief for the Los Angeles Fire Department. “Arsonists usually aren’t going to go 500 feet off a trailhead through trees and brush, set a fire and then run away.”

Fires break out in the wooded areas on the edges of Los Angeles all the time — many of them caused unintentionally by homeless people. The fires almost never grow into a destructive blaze due to the lack of high winds. The combination of ferocious winds and a parched landscape created ideal conditions for the fast-moving fires that have consumed large swaths of Los Angeles this week.

“You don’t need a gang of arsonists to go out there and be starting fires because nature is taking care of that for you,” said Scott Fischer, a retired federal law enforcement arson investigator.

“There are arsonists out there,” he added, “but are there a band of arsonists running around Los Angeles right now? Not likely.”

Copycat arson is a known phenomenon, however. The experts said they wouldn’t be surprised if one of the smaller fires that broke out after the Palisades blaze was intentionally set.

“When you get a large fire event like this being experienced in Los Angeles, you sometimes trigger people to go out and light a fire,” said Terry Taylor, a retired wildland fire investigator who now works as an instructor. “It’s a copycat thing. … It happens from time to time.”

Taylor and the other experts said it’s unlikely those answers will come anytime soon, as determining arson tends to require a lengthy investigation.

Eaton Fire

The Eaton Fire, the second largest to wreak havoc in Los Angeles, is not one of those likely to have been started by an arsonist, the experts say. It erupted Tuesday evening in an area east of Altadena where an array of high-voltage transmission lines hovers overhead.

Given the area and weather conditions, the fire experts said their first thought was power lines. Whipping winds can cause the lines to slap together, shedding small balls of superhot molten metal.

“If the ground is really dry and the wind is blowing and poof — you have a fire,” said Ed Nordskog, a retired detective with the Los Angeles County Sheriff’s Department who spent his career investigating arsonists.

But that’s just one potential scenario. It’s also possible that it was started by a person operating a camping stove or a car or lawn mower that ejected a hot spark onto dry grass, Nordskog said.

As for the possibility it was intentionally set, Nordskog said it was unlikely.

“Most of the time, these fires are not arson,” he said. “There is no data supporting winds bringing out arsonists.”

‘Inch by inch’

Identifying the cause of a fire is a highly specialized and painstaking endeavor, experts say.

The first step is pinpointing where it began. Things like burn patterns and charred debris can provide crucial clues.

Then comes the most detailed and labor-intensive part of the process. The investigators will lay out a grid at the scene, typically with string, and literally crawl around on their hands and knees in search of footprints or other clues.

The investigators often use metal detectors and magnifying glasses or even binoculars to help with their search.

“They’ll go inch by inch by inch, and it will take hours,” said Nordskog. “It’s not fun.”

In the case of the Eaton Fire, the investigators are likely to use magnets to help them hunt for the tiny, melted pieces of metal that could have been shed by power lines if they slapped together. But the existence of the metal doesn’t necessarily indicate that’s how the fire started, Nordskog said.

“You still have to figure out if the power lines’ spark was because things were already on fire or what started the fire,” he said.  “There’s so much stuff going on with an investigation, so many factors. Anybody tells you right away what caused the fire, they had to have seen it.”

If the investigators find evidence the fire was caused by a person, they must then work to determine whether it was the result of an accident, negligence or an intentional act.

John Abatzoglou, a professor of climatology at the University of California, Merced, examined 30 years’ worth of government fire occurrence data from Los Angeles County. It showed that the most common causes of wildfires from 1992 to 2020 were mishaps related to vehicles and other equipment.

“More than 95% of these are human-ignited fires,” he wrote in an email. “Arson is among the causes, but most human-caused fires are not intentional.”

‘The best players out there’

The prospect of arsonists torching Los Angeles gained traction on social media Thursday when a group of people in Woodland Hills detained a man they suspected of setting a trash fire. The man was arrested, but there was not enough probable cause to charge him with arson, police officials said Friday. He was arrested on a felony probation violation instead.

In addition to the Palisades and Eaton fires, four others have burned across Los Angeles. The causes remain under investigation.

A law enforcement task force has been set up to uncover what caused the fires. The local agencies involved — the Los Angeles fire and police departments and the county Sheriff’s Department, as well as Cal Fire — are considered to be among the most skilled in the country. The Bureau of Alcohol, Tobacco, Firearms and Explosives is leading the probe.

“Everything is absolutely on the table,” Los Angeles County Sheriff Robert Luna said at a news conference Saturday.

It could take several days for investigators to determine the causes of the fires. Determining whether a fire found to have been started by a person is a criminal act could take several months or even years, the experts said.

With the number of fire deaths reaching 24, the effort to uncover the causes is expected to go on for as long as it takes.

“You’re going to have the best players out there to be able to solve the problem,” said Crawford, the retired Los Angeles battalion chief.