Federal law enforcement officials accuse Jonathan Rinderknecht of lighting a fire on New Year's Day that was initially extinguished by fire crews, but continued to smoulder underground before reigniting during high winds, acting US Attorney Bill Essayli said.
Rinderknecht was arrested in Florida on Tuesday and is due to appear in court on Wednesday.
He faces charges including malicious destruction by means of a fire.
Rinderknecht fled the scene of the original fire, but returned to the same trail to watch it burn, Essayli said.
"He left as soon as he saw the fire trucks were headed to the location. He turned around and went back up there. And he took some video and and watched them fight the fire," Essayli said
Rinderknecht also made several 911 calls to report the fire, according to a criminal complaint.
During an interview on January 24, Rinderknecht told investigators where the fire began, information not yet public and that he would not have known if he hadn't witnessed it, the complaint said.
He lied about his location, claiming he was near the bottom of the hiking trail, Essayli said.
The suspect was visibly anxious during that interview, according to the complaint.
His efforts to call the emergency service hotline and his question to ChatGPT about a cigarette lighting a fire indicated he "wanted to preserve evidence of himself trying to assist in the suppression of the fire and he wanted to create evidence regarding a more innocent explanation for the cause of the fire," the complaint said.
Investigators determined the January 1 fire was intentionally lit, likely by a lighter taken to vegetation or paper, according to the criminal complaint.
They excluded other possibilities, including fireworks, lightning and power lines.
Authorities also looked into whether a cigarette may have caused the fire, but concluded that it was not the cause, the complaint says.
Investigators found a "barbecue-style" lighter inside the glove compartment of Rinderknecht's car on January 24.
It appeared to be the same lighter as the one that was in his apartment on December 31, based on a photo on his phone.
He admitted to bringing a lighter with him when he walked up the hill.
The blaze, which erupted on January 7, killed 12 people and destroyed more than 6000 homes and buildings in the Pacific Palisades, a wealthy coastal neighbourhood of LA.
The fire ripped through hillside neighbourhoods, destroying mansions with spectacular views of the ocean and downtown LA.
Investigators still haven't determined the cause of a second blaze called the Eaton Fire, which broke out the same day in the community of Altadena and killed 18 people.
Both fires burned for days, reducing block after block of entire neighbourhoods to grey and black debris.
An outside review released in September found that a lack of resources and outdated policies for sending emergency alerts led to delayed evacuation warnings.
The report commissioned by Los Angeles County supervisors said a series of weaknesses, including "outdated policies, inconsistent practices and communications vulnerabilities," hampered the county's response.
