An investigation into the second of two fatal grizzly bear attacks last summer at Yellowstone National Park was unable to conclude if the same bear was responsible for both deaths, a report released Monday said.

Brian Matayoshi, 57, was killed July 6. His death was witnessed by his wife, Marylyn Matayoshi.

John Wallace, 59, was likely killed Aug. 25. He was alone, so there is no one to verify the time or date. A bear also fed on him.

According to a concession employee who checked him into a campground, Wallace said he was knowledgeable about bears. Family members said he was an experienced outdoorsman and backcountry hiker, the report said.

There were two bison carcasses and five grizzlies in the Mary Mountain Trail area where Wallace was killed, but there is no definitive evidence that the sow grizzly that killed Matayoshi and was later destroyed was responsible for Wallace’s death.

“There is no way to know which specific animal killed Mr. Wallace,” said Al Nash, Yellowstone spokesman.

However, based on DNA evidence, they do know the sow responsible for Matayoshi’s death on Wapiti Lake trail also was at the site of Wallace’s death on Mary Mountain trail between the time of the incident and the discovery of his body, Nash said.

Mary Mountain trail is south of Canyon Village on the northern edge of Hayden Valley. Wapiti Lake trail is south of Canyon Village off the Artist Point spur road.

Following Wallace’s death, about a dozen grizzlies were captured around the Canyon area. On Sept. 28, the sow that killed Matayoshi was caught, along with her two cubs. She was euthanized Oct. 2 and her cubs were placed under the care of the Grizzly and Wolf Discovery Center in West Yellowstone, Mont., Nash said.

Bears were feeding on bison carcasses around the time and a grizzly may have attacked to protect its cache, but that is speculation too, Nash said.

“We just don’t know what prompted a bear attack on Mr. Wallace,” Nash said.

The report speculates that Wallace was stopped at the time of the attack, but what motivated a grizzly strike will never be known because there is no living witness.

Wallace appears to have taken off his daypack and may have been snacking on an energy bar when he was attacked.

Bite marks on his hand and arm indicate that Wallace tried to fight back, but he was not carrying bear spray.

Wallace’s final moments were likely terrifying.

“Bruising associated with some of the wounds indicated that Mr. Wallace was alive at the time some of the wounds were inflicted,” said the report.

“The body had been partially consumed and exhibited canine bite wounds and other injuries consistent with a bear attack,” the report said.

A father and daughter hiking along the trail the next morning found Wallace’s body partially on the trail and partially buried next to the trail “consistent with the food caching behavior of a bear,” the report said.

The night before the attack, campground personnel gave Wallace a lecture about food storage and bear safety when he arrived at the Canyon Village campground. Wallace said that “he did not need to hear that information and that he was a ‘grizzly bear expert,’” the report said.

A sign posted at the Mary Mountain trailhead warned hikers that they were entering bear country, recommended carrying bear spray and recommended against hiking alone.

Matayoshi’s wife witnessed the fatal attack on her husband. The official report in that fatal July mauling suggested that the Matayoshis were running from the grizzly, and that may have incited the attack.

(The Associated Press contributed to this story.)