The FBI, U.S. Marshals and Montana police are hunting a former militia leader, considered armed and dangerous.
Officials have been canvassing the rural region where David Burgert disappeared Sunday, searching highways and keeping watch over Flathead County, Mont., where they anticipate he might return. But so far, he has managed to elude authorities.
"Needle in a haystack right now, but we're trying," Missoula County Undersheriff Mike Dominick said.
"He is dangerous to the public," Flathead County Undersherriff Jordan White told ABCNews.com. Though Burgert's "primary aggression has been towards government agencies," White said he might steal equipment, food or even another vehicle from citizens. He is alleged to have stolen the guns he has in his possession.
The search for Burgert, 47, started Sunday, when officers followed up on a call they received about the ex-convict, who is under federal and state probation after being released from prison. Dominick said Burgert had been living in his car at various campsites.
When police arrived at the park, Burgert fled.
They chased him up a rural highway in a mountainous pass near the Idaho border. Burgert stopped his vehicle on a county road and fired rounds at deputies with a handgun before running into the 2.1 million acre Lolo National Forest, a region with rolling hills and -- in some areas -- heavy vegetation.
"Sometimes it's even difficult to see 100 feet in front of you, so it's definitely slow to move through," Lolo National Forest spokesman Boyd Hartwig said.
After Burgert abandoned his first vehicle outside the forest, police found a second car stocked with survival equipment and firearms, near the town of Lolo.
Officials said Burgert might currently be in his third vehicle, which they have not yet located, a 1987 Jeep Wagoneer.
Burgert's Stepmother: 'You Would Think He's the Sweetest Person Alive'
Burgert's stepmother Sandra Burgert, 67, said she's "flabbergasted" at the latest news.
"He made good grades in school, he got along with people," said Sandra Burgert, who lives in Mount Dora, Fla. "He likes his trucks, and he was a survivalist, he just tended to be that way."
When the family lived in Colorado, she said, "his only hobby was collecting guns when he was 19."
"He never seemed to be depressed," she added. "You meet him you would think he's the sweetest person alive."
Sandra Burgert said she last spoke to her stepson in the early '90s, and described his family life as troubled: His grandfather reportedly committed suicide and his biological mother, who used to be a nurse in the army, had her own run-ins with the law.
David Burgert, who used to be in the Marines, went AWOL, according to his stepmother, in the early '80s.
The stepson she knew had a good personality and was a "very likable, very handsome young man."
"He was just in and out between staying with his mother and father, he didn't let any grass grow under his feet, he kept moving," she said.
Burgert's Ties to Project 7
For the past two decades, however, Burget has been arrested several times. He was charged with assaulting Flathead County deputies in 2001 and Undersherrif White said police ultimately discovered his disturbing goal: to "start a revolution."
Investigators learned Burgert was leading Project 7, a militia group named after Flathead County, which is the seventh county in the state.
"He had organized a group of people with the plan that they would assassinate elected officials and law enforcement officers in Flathead County, which would cause, eventually, an emergency declaration and involvement of the National Guard and they'd be able to declare war against the U.S. military," White said.
When police found Burgert in 2002 he was prosecuted and sentenced to federal prison, White said.
Before that arrest, Flathead County Sheriff Chuck Curry told the AP, Burgert had attempted to escape authorities by staging his own death. When officers eventually found Burgert, they chased him all night before cornering him. Burgert held a gun to his head before surrendering, Curry said.
White said Burgert also had a number of less dramatic arrests and charges that culminated in the late '90s, when he was renting snowmobiles and boats and conducting guided tours in the forest without a permit.
Domestic Terrorism in Montana
In April, then FBI Special Agent in Charge James McTighe, who led the FBI's Salt Lake City office overseeing Montana, Idaho and Utah, told Montana's KRTV that domestic terrorism is a big concern in the state.
"Some of the groups in the state of Montana espouse violent overthrow of the government. I don't have any that I would name right now, just suffice it to say that it is a matter of keen interest to us," McTighe said at the time. "I think we have a good understanding from an international terrorist perspective of what the threats are in the state of Montana. I wouldn't equate them to what the threat would be, for example, in New York City, or Los Angeles, or Washington, D.C."
The FBI declined to comment for this story.
Dominick said Burgert is 6 feet 2 inches tall, and weighs at least 230 pounds, possibly 250. He has brown eyes and brown hair, and was last seen wearing a bluish shirt, khaki pants, and a fanny pack. Police believe he is armed with a handgun and possibly a rifle.
If anyone has information about Burgert or his whereabouts they can call the Flathead County Sherriff's office at 406-758-5610.
ABC News' Joanna Suarez and Bonita Sostre and The Associated Press contributed to this report.