MELBOURNE, Florida — The alleged firebug accused of starting the Palisades blaze threatened to burn down his sister’s house and shoot his brother-in-law with a gun he stashed in a stuffed animal, according to authorities.

Jonathan Rinderknecht’s alleged threats concerned his family so much that they moved out of the house to get away from him and reported him to the police, the feds revealed Thursday.

The disturbing revelations came Thursday morning during an Orlando federal court hearing for the 29-year-old — accused of igniting the most expensive wildfire in US history — where an agent for the US Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) testified about alarming behavior from just last month.

And it’s just the latest in a long life of bizarre behavior from the Biden-supporter, whose social media reveals Trump-hating virulence and hypocritical eco-apocalypse posting.

Rinderknecht — shackled and wearing red jail clothes — looked on during the testimony as his brother and two sisters sat in the courtroom gallery. One of the sisters began crying when Magistrate Judge Nathan Hill said Rinderknecht would be kept behind bars.

Prosecutors also revealed he could potentially face the death pentalty if convicted of setting a fire that caused death.

Cops were twice dispatched to Rinderknecht’s sister’s home in central Florida last month — once after he allegedly threatened to torch his sister’s house, and once when he threatened to shoot his own family,  ATF agent Thomas Harrison testified.

Rinderknecht moved from Los Angeles back to his home state of Florida after allegedly starting the blaze that would grow into the Palisades Fire.

He settled in with his sister and brother-in-law outside Orlando – in a three-bed, two-bath, $500,000 home located in a gated community. 

Neighbors told The Post they’d seen Rinderknecht — even as his pattern of unhinged behavior allegedly escalated.

Rinderknecht’s sister’s kids were even moved out of the house after he moved in and the family grew concerned over his rapidly declining mental health, according to the testimony Thursday.

Rinderknecht allegedly threatened to shoot his brother-in-law, prompting his father to call the cops – with investigators allegedly finding a gun hidden within a stuffed animal when they searched the home.

The alleged firebug claimed he made the threat in self-defense and had the gun locked in a safe, not in a plushie. Cops did not make an arrest after either visit last month.

Rinderknecht was living in Los Angeles in January when he allegedly took a car to the Palisades Hills and set a blaze in a popular hiking area – then reported it to authorities and returned to the site to watch firefighters battle it, according to authorities.

The fire continued to smolder after firefighters left, and it exploded days later into the deadly Palisades blaze, federal prosecutors said.

Alleged arson aside, strange behavior seemed to follow Rinderknecht in LA as it did in Florida.

On he same day the Palisades fires exploded — Jan. 7 – Rinderknecht was sued for causing a motorcycle crash that left the rider with gruesome injuries, court documents show.

Rinderknecht was driving for Doordash in the summer of 2024 when he made a wide left turn in his Volkswagen, smashing into a man on a motorcycle. The crash left the biker with lasting injuries, including neurological damage he may never recover from, that suit claimed.

Then, in March – after the Palisades flames finally died down – Rinderknecht filed a lawsuit accusing a crack-smoking male neighbor of repeatedly stalking him, then luring him to his apartment and attempting to sexually assault him while watching violent porn at full volume.

His social media was also filled with eyebrow-raising posts, including a photo of himself with wild-eyes and his face painted like a blood-covered skull.

But eeriest of all were the eco-apocalyptic articles he routinely shared – which included a ProPublica story titled “Climate Change Will Force a New American Migration” about wildfires forcing mass displacements in California. 

The story featured a photo of a California neighborhood nearly engulfed in flames raging on surrounding hills.

Other posts included headlines like “Antarctica’s Ice Shelves Have Lost Millions of Metric Tons of Ice,” from Scientific American, “Senator Kamala Harris Says Meat is Destroying the Planet” from another outlet, and “Ocean Plastic Could Triple by 2040 and Outnumber Fish by 2050,” from the Independent.

Rinderknecht also appeared to be a virulent Trump opponent – at one point even sharing a reel of MAGA crowds apparently crying when the president lost the 2020 election, and another time sharing a Biden-Harris campaign fundraiser.

During the 90-minute hearing Thursday, Magistrate Judge Nathan Hill ordered Rinderknecht to be held without bail until his trial, citing mental health concerns, sporadic income and his rocky relationship with his family members, according to a report by Orlando Sentinel.

Hill said while there wasn’t “clear and convincing” evidence that Rinderknecht would hurt anyone, he couldn’t let him go free because he’s a flight risk, the outlet reported.

“When I look at that altogether, I find there is a preponderance of evidence that there are no conditions that will ensure your presence at future hearings,” Hill said.

The judge also noted the seriousness of the crimes Rinderknecht was charged with and the additional crimes he’s expected to be hit with. 

Orlando Special Assistant US Attorney Rachel Lyons said any further charges could prompt prosecutors to seek the death penalty in his case.

“It’s extraordinarily serious, and I agree with Ms. Lyons that the higher the severity of the offense, the greater the risk of fleeing,” Hill said. “What I don’t want to do is release you, setting you up to fail.”

Earlier in the hearing, Lyons described Rinderknecht as a financially struggling loner with “a despondent view of the world,” whose mental health declined at a time when he drifted from his closest relationships.

“He struggled socially without many friends,” having fallen out with old friends and broken up with his girlfriend around the time of the fire, Lyons said.

Rinderknecht also allegedly had troubling conversations with ChatGPT, including asking the chatbot during a 911 call reporting the fire: “Are you at fault if a fire is lift [sic] because of your cigarettes?” according to an affidavit.

And just months before the fire, he asked the artificial intelligence platform to generate an image of a burning city and he told the chatbot he “literally burnt the Bible that I had. It felt amazing. I felt so liberated.”

Despite the seemingly incriminating evidence, Lyons said during a Jan. 24 interview with investigators Rinderknecht waffled on his involvement in starting the catastrophic fires.

But the officers observed that an artery on his neck would “pulsate and become visible whenever they asked Rinderknecht a question about how the fire started and who started it,” an arrest affidavit said. 

Lyons said Rinderknecht was a flight risk because of his family ties to France where he was born, the fact his passport was missing and that he’d messaged his ex-girlfriend saying he wanted to flee to Bali, Indonesia.

Rinderknecht cast his eyes downward and swayed back and forth in his chair, occasionally shaking his head when Lyons spoke.

Rinderknecht’s defense attorney, Public Defender Aziza Hawthorne, told the judge he’d started seeing a psychiatrist and had begun taking medications.

The lawyer requested that he be released to home confinement at his sister’s home where he would be monitored until trial, noting he didn’t face any accusations of physical violence.

“They said they will support him in any way they can, and that means financial and emotional support,” Hawthorne said.

The defense attorney also argued that the court papers against Rinderknecht contained “paragraph after paragraph after paragraph of circumstantial evidence.”

And Hawthorne said the incidents from last month weren’t criminal and that Rinderknecht had no prior arrests. She also said he didn’t have the money it would take to flee abroad.

The judge disagreed, and ordered that Rinderknecht remain in custody.

Federal-level arson charges like Rinderknecht currently faces carry prison terms up to 20 years, but penalties can increase when injury or death are involved.

With Post wires