According to the press release:
"Montana Fish, Wildlife, and Parks staff members believe the animal tripped while trying to cross a fence and somersaulted onto his back, where he was pinned between rocks with his antlers beneath him and suffocated."
In the photo below he is standing on a travertine terrace near park headquarters in Mammoth Hot Springs. Although not plainly visible in this photo, he had a small orange tag with the number six on it, in his left ear.
Park Officials believed the elk was at least fifteen years old. His antlers were cut off during the rut of 2004 and 2005 to reduce the risk that he would injure persons or damage property. He was known for "horning" vehicles and chasing unwary tourists.
During our visit, the rut was already underway and park rangers were exercising tight crowd control to keep the tourists and the elk separated. Persons are required to stay at least 25 yards away from most animals and 100 yards away from bears and wolves.