A grizzly bear that mauled three campers outside Yellowstone National Park had parasites and was struggling to feed her cubs, according to a report released Monday.

But state and federal wildlife investigators said those factors alone were not enough to explain such predatory behavior.

"We looked at food habits, body condition of the bear, past behaviors — none of those stand out as a reason that would indicate why this bear would do this," said investigation leader Chris Servheen with the U.S. Fish and Wildlife Service.

Kevin Kammer, 48, of Grand Rapids, Mich., was killed and two people were hospitalized when the 216-pound grizzly tore into their tents in a nighttime attack July 28.

The bear was captured a day later at the Soda Butte Campground near Cooke City, then was euthanized. Its three cubs are now in a Billings zoo.

DNA tests on strands of hair found at the campground linked the mother bear to the attacks. Tests for rabies and other diseases came back negative following a necropsy.

Investigators blamed a vegetarian diet on the mother grizzly's poor body condition, which they said was "made worse by a load of parasites found in her small intestine."

There was no sign the bear had become habituated to humans, which is often to blame when bears have run-ins with people.

It had been sighted around the Cooke City area at least twice, but the necropsy results showed no signs the bear had eaten human food over the last two years.