The search for a grizzly bear that killed a mountain biker in Montana has been called off after an investigation found a collision was to blame.

Wildlife response team investigator Brian Sommers believes Treat was riding at a high rate of speed with poor visibility along a narrow trail and hit the bear. Authorities believe the collision was unavoidable and the cameras and bear traps being used to find the bear have been removed.

Brad Treat, 38, and another rider were riding in the Half Moon Lakes area of the Flathead National Forest on Wednesday when they reportedly surprised the bear and it attacked Treat. He was knocked off his bike and his fellow rider went to look for help.

Treat's body was found at the scene but the bear was nowhere to be seen. Treat was a law-enforcement officer for the US Forest Service. Chuck Curry, Flathead County sheriff, said: "Brad was an integral member of our area law enforcement team and a friend to us all."

Grizzlies have been designated a threatened species in the area since the 1970s, but as their numbers increase and so so conflicts between humans and bears. Before this attack there had been 10 bear-related human deaths in Glacier since the park was created in 1910. The last was in 1998, when three bears killed and partially ate a park employee while he was hiking.

In the most well-known Glacier attacks, bears killed two people in different parts of the park in a single night in 1967. Those attacks became the subject of a 1969 book by Jack Olsen titled “Night of the Grizzlies," and later a documentary by the same name.