A mountain goat that fatally gored a hiker, then stood over the man and stared at people trying to help, had shown aggressive behaviour in the past, US Olympic National Park officials said.
Robert Boardman, 63, of Port Angeles, died on Saturday after he was attacked by the goat while hiking on the subalpine Switchback Trail in the park.
The trail is popular with residents of nearby Port Angeles, which is about 85 miles west of Seattle.
Park rangers later found the goat, observed blood on it and shot the animal.
Rangers have been tracking the goat and others for the past four years because they have followed people or approached hikers without backing down, said park spokeswoman Barb Maynes.
"It has shown aggressive behaviour, however, nothing led us to believe it was appropriate to take the next level of removal," she said.
"This is a highly unusual. There's no record of anything similar in this park. It's a tragedy. We are taking it extremely seriously and doing our best to learn as much as we can."
Park officials have posted signs at trailheads warning hikers to be watchful of all goats and to stay at least 100 feet from the animals.
Hikers are also warned not to urinate on or near the trail, because goats are attracted to the salt.
A necropsy, or animal autopsy, was conducted on the goat on Sunday night by a private certified veterinary pathologists. Park officials are awaiting test results of blood and tissue samples, which may take a couple weeks, Ms Maynes said.
"We're looking for anything to indicate any presence of diseases, which might shed light on the animal's extremely strange and unusual behaviour," she said.
Mr Boardman was hiking with his wife, Susan Chadd, and their friend, Pat Willits, and had stopped for lunch at an overlook when the goat began acting aggressively toward them, the Peninsula Daily News reported.
Mr Boardman urged the others to go ahead while he tried to get rid of the goat, according to the paper. The two heard him yell and ran back to help.
Hikers who came upon the group radioed for help. But it took nearly an hour before rescuers could reach Mr Boardman because the goat stood over him as he lay motionless on the ground, according to the Seattle Times.
"The mountain goat was terribly aggressive," Jessica Baccus, who was hiking with her family, told the Times. "It wouldn't move. It stared us down."
She and her husband, Bill Baccus, a park scientist, tried to lure the goat away by pelting the animal with rocks, shouting at it and using a silver reflective blanket to distract it.
It finally moved away, and Jessica Baccus tried to give Mr Boardman cardiopulmonary resuscitation until a local doctor who came upon the group took over, she told the Times.
A US Coast Guard helicopter airlifted him out of the park.
Mr Boardman, a locally-known musician and diabetes educator, was an avid hiker who also worked for years as a nurse for the Makah and Lower Elwha Klallam tribes, according to the Peninsula Daily News.