Rescue crews are continuing to search for a former Navy SEAL after his half brother's body was recovered in Yellowstone National Park on Monday (September 20).
Kim Crumbo, 74, of Ogden, Utah, and Mark O'Neill, of Chimacum, Washington -- both retired from the park service -- were reported missing by a relative on Sunday (September 19) after never returning home from a four-night backcountry trip, the National Park Service confirmed to NBC News.
On Monday, O'Neill's body was located on the east shore of Shoshone Lake, the second largest at Yellowstone, the National Park Service confirmed.
No cause of death has been released for O'Neill as of Wednesday (September 22) morning.
"On Sunday, Sept. 19, park crews located a vacant campsite with gear on the south side of Shoshone Lake, as well as a canoe, paddle, PFD and other personal belongings on the east shore of the lake," the NPS said in a statement obtained by NBC News regarding the search that led to O'Neill's body being discovered the following morning.
Authorities continued to search for Crumbo on Tuesday, which included 10 crew members on the ground and a helicopter observing an aerial view.
The former Navy SEAL spent two decades working as a river ranger, park ranger and wilderness coordinator in Grand Canyon National Park, the Salt Lake Tribune reported amid news of his disappearance.
Crumbo is also a "proud Citizen Member of the Potawatomi Tribe" and a board member of the Rewilding Institute, according his bio page on the conservation program's official website.
Crumbo also frequently contributed to the Salt Lake Times with letters to the editor calling for the protection of "wolves, wild horses and the environment."
The National Park Service said the average year-round temperature at Shoshone Lake is about 48 degrees and survival time is estimated to be only 20 to 30 minutes in water when temperatures drop that low.