Updated

Federal prosecutors have decided not to file charges against two young elk hunters after investigators concluded they acted in self-defense when they shot and killed a grizzly bear in Grand Teton National Park last fall, park officials announced Thursday.

The bear charged the two and their father from 42 yards on Thanksgiving Day. First, the father fired bear spray at the animal. The sons opened fire when the bear was 10 feet away.

Three bullets — one to the back and two to the head — brought down the 534-pound male practically at the hunters' feet.

"The hunters were in the correct hunting area with appropriate hunting licenses," John Powell, a spokesman for the U.S. Attorney's Office in Cheyenne, said by email. "They immediately reported the incident and cooperated fully with the investigation by US Fish and Wildlife officers."

Grand Teton officials did not identify the hunters, but the Jackson Hole News & Guide previously identified them as David Trembly, 48, of Dubois, and his 20- and 17-year-old sons, who remain unidentified.

Trembly did not immediately return a message seeking comment.

A grandfather of the boys, Dwayne Trembly, of Cheyenne, said Thursday he was about 300 yards away from the trio when the grizzly was shot. The elder Trembly said trees blocked his view of what happened.

He said he had already heard that investigators had exonerated his grandsons.

"They complimented the boys on how well they did because the bear was within eight feet of one of them," Dwayne Trembly told The Associated Press.

Grizzlies are listed as threatened under the Endangered Species Act. Shooting one, except in self-defense, is punishable by up to a year in prison and fines up to $50,000.

Park rangers investigated the shooting in cooperation with the U.S. Fish and Wildlife Service, which enforces federal wildlife laws and regulations. Investigators found a partially eaten and cached elk carcass about 50 yards from where the shooting occurred and concluded that the grizzly charged to defend the food source, according to a Grand Teton news release.

The hunters had begun their trip at the parking area at Schwabacher Landing at first light. David Trembly first saw the bear soon after they entered a wooded area in the Snake River bottoms and tried to scare it off.

All three hunters had ready access to bear spray. When the bear charged, David Trembly fired his spray while his sons raised their rifles and initially held fire. One of the hunters described he grizzly bear as moving "incredibly fast" and "like a cat," moving low to the ground and snapping branches as it charged, according to the release.

Grand Teton is one of the few national parks that allow hunting. The annual fall elk hunt helps wildlife managers control the size of the local elk population.