Robert "LaVoy" Finicum, a rancher who acted as a spokesman for the self-identified militia that has illegally occupied a federally owned wildlife refuge in Oregon since January 2, was killed on Tuesday during a confrontation with US authorities. His death has been taken up as a cause by anti-government activists.

The FBI said gunshots rang out after officers stopped a car carrying protest leader Ammon Bundy and others near the Malheur National Wildlife Refuge. Finicum was fatally struck, while Ammon Bundy's brother Ryan suffered a minor gunshot wound.

On Thursday, the FBI released footage of the incident — 26 minutes of unedited video.

Federal officials said they had probable cause to arrest Finicum, who told NBC News earlier this month that he would rather die than be detained.

The FBI said that Finicum was armed when he was stopped, and that the video shows him reach for his jacket pocket before he was shot dead by law enforcement after speeding away from the traffic stop.

The aerial video taken by law enforcement helicopters showed Finicum speed off in a white truck from FBI and Oregon state police and nearly strike a law enforcement officer while trying to evade a police barricade before barreling into a snowbank and exiting the car.

The grainy aerial footage shows Finicum raise his hands in the air and then turn and flail his arms moments before he is shot by an officer the FBI identified as a state trooper.

Greg Bretzing, special agent in charge of the FBI's Portland office who narrated the video for reporters, said Finicum can be seen reaching for his jacket pocket. But a lack of focus in the video makes Finicum's precise movements prior to the shooting difficult to discern.

The agents and officers do not attempt to administer first aid or attend to Finicum until roughly 10 minutes after he is shot and lying down.

Bretzing told reporters at an evening news conference in the rural community of Burns, Oregon that while the video showing Finicum's death was potentially upsetting, it was released in the interest of transparency.

The occupation began when leader Ammon Bundy and at least a dozen of his followers took over a small cluster of buildings at the refuge on Jan. 2 in a flare-up in the so-called Sagebrush Rebellion, a decades-old conflict over federal control of millions of acres in the West.

Police and federal agents kept their distance from the site, 30 miles (48 km) from the small town of Burns in Oregon's rural southeast, in an effort to avoid a violent confrontation.

But on Tuesday, Bundy and his leadership team left the refuge to speak at a community meeting in John Day, Oregon, and were stopped by law enforcement. The stop led to Finicum's fatal shooting and the arrest of Bundy along with four others.

Bundy and the other senior members were taken into custody following the confrontation along Highway 395, near the reserve in northeast Oregon around 4:25pm local time. All of those arrested face federal charges of conspiracy to use force, intimidation or threats to impede federal officers from discharging their duties, the FBI said.

The FBI set up a perimeter around the refuge where a few people were still holding out, continuing their protest against federal control of large tracts of the country.

Jason Patrick, who was one of the remaining occupiers, told Reuters by phone earlier this week that they would stay until the "redress of grievances." "I've heard 'peaceful resolution' for weeks now and now there's a cowboy who is my friend who is dead — so prepare for the peaceful resolution," Patrick said.

Patrick likened Finicum's death to the killing of Tamir Rice, an unarmed 12-year-old African-American boy fatally shot by police outside a Cleveland recreation center in 2014. The officers were not charged. "The government can kill who they want for whatever reason they want with impunity," Patrick said.

Patrick was taken into custody after turning himself in at around 8:40pm Wednesday night at a roadside checkpoint near the refuge. Two other militia members, Duane Leo Ehmer, 45, and Dylan Wade Anderson, 34, also surrendered to police earlier that afternoon. 

Bretzing said four occupiers remained holed up at the refuge compound on Thursday night, as authorities sought to negotiate with them to leave.