Editor's note: Portions of the following story are graphic and might not be suitable for everyone.

A Michigan man fatally mauled and partially consumed by grizzlies in Yellowstone National Park last summer was hiking through a landscape with a high concentration of bears, some no doubt drawn by the presence of two bison carcasses, according to a Board of Review investigation into the attack.

John L. Wallace, of Chassell, had set out for a dayhike on the Mary Mountain Trail about 7:30 a.m. last August 25 and apparently had stopped for a snack or perhaps a drink of water about 5 miles from the trailhead when he was attacked, the report released Monday noted.

The 59-year-old tried to ward off the grizzly, as evidenced by lacerations an punctures on his right forearm, the investigators determined.

The attack occurred in an area of mixed lodgepole pine, meadows, and rolling hills that the trail passes through. A father and daughter out hiking the trail the following day found his body, which had been cached under duff and debris, a common practice of bears intent on returning to a kill.

"I was hiking a little in front of my dad," the young woman wrote in a statement she provided rangers. "The trail started to go into some timber and there were five or six birds circling above the area. I climbed over a log that was across the trail and that is when I saw a plastic clear drink container with some pink liquid in it and what I thought was a backpack.

"As I got closer I realized there were boots sticking out, legs, and the upper part of the body was covered with dirt," the unidentified woman continued. 

Mr. Wallace was found on his back, his feet sprawled across the trail. His daypack had been pulled atop his body, along with the duff and dirt, while his rain jacket, two water bottles, and a plastic lunch container were nearby.

The attack was the second fatal mauling in the park last year and marked the first time anyone could recall two fatal maulings in one year in Yellowstone.

Nearly two months earlier another visitor, 58-year-old Brian Matayoshi from Torrance, Calif., was out for an early morning hike with his wife on the Wapita Lake Trail near Canyon Village when he was run down and killed by a sow grizzly that investigators determined was exhibiting normal defensive behavior.

In the Matayoshi mauling, the sow had two cubs nearby and stopped the attack once she determined the man was no longer a threat, according to an investigation into that attack.

Investigators looking into the Wallace mauling were able to conclude from DNA analysis of scat that the sow that killed Mr. Matayoshi was at the scene of Mr. Wallace's death, but couldn't say for sure that she was responsible for his death. 

"The presence of bloody adult and cub tracks suggests that the adult female that killed Mr. Matayoshi and one of her offspring were likely involved in the consumption of Mr. Wallace's body," the report noted. "However, there could have been other bears involved in the consumption of Mr. Wallace."

The investigation could not pinpoint a cause for the attack on the Michigan man.

"Mr. Wallace was either stopped along or adjacent to the trail or stopped in reaction to a close encounter with a bear(s) at the time he was attacked," noted the report, which was prepared by a team of wildlife experts from the U.S. Fish and Wildlife Service, the National Park Service, and the states of Montana and Wyoming.

"He tried to defend himself from the attacking bear, as evidenced by bite marks to his hands and arm. Portions of his body were consumed during the approximate 24-hour period between when he was killed and when his body was initially found by two hikers the next day. There is DNA evidence of at least four different grizzly bears at or near (within 150 meters) the site where his body was found," the report went on.

Following the attack on Mr. Wallace, park crews set up a trapping operation to see if they could catch the grizzly responsible for his death. A number of grizzlies was eventually caught, hair samples were taken for DNA analysis, and the bears released with radio collars so they could be tracked and, if necessary, recaptured if a match was made.

In late September the female grizzly connected with the two maulings was captured along with her cubs. While the cubs were placed in the Grizzly & Wolf Discovery Center in West Yellowstone, Montana, the 250-pound sow was euthanized on October 2. She was not relocated to the Discovery Center with her cubs, park officials said, because (A)dult bears that are removed from the wild do not adapt well to captivity."

While Mr. Wallace had told a campground concessions worker the day before his death that he was a "grizzly bear expert," the man was hiking alone in an area with a high concentration of grizzlies apparently without any bear spray, the investigators found.

Two bison carcasses were nearby; one was 330 meters to the southeast of the attack site and was surrounded by 16 bear beds, the report said. The other carcass was about 1.5 miles away from the attack site and near the trail, it added. "Nine different grizzlies, including a female with two cubs-of-the-year, were observed by a day hiker on August 22 at this second bison carcass, three days before Mr. Wallace was killed," the report said.

Though the landscape where Mr. Wallace was attacked was fairly open, visibility was hampered by its rolling nature and vegetation, according to the investigators.

"A bear approaching from the from the north from the direction of the trailhead would have been partially obscured by a large lodgepole next to the trail," the report reads. "There is no clear evidence what prompted the bear(s) to attack Mr. Wallace."

Yellowstone hosts over 3 million visitors a year, with an average of just one bear-caused human injury a year. Since the park was established in 1872, there have only been seven recorded fatal maulings, according to Al Nash, the park spokesman.

Yellowstone officials are evaluating the wildlife warnings they give park visitors, Mr. Nash said Monday, and while they believe they already deliver a strong message about bears, they "are looking to see if we can improve how we share this message with visitors."

"Two areas I can cite specifically that we are working on are our trailhead signs and our park newspaper," the spokesman said.