A group of river rafters in Grand Canyon National Park have reported finding plane wreckage with human remains inside during a May 20 trip near Emerald Canyon. Park rangers were able to recover the skeletal remains and the plane on Sunday. A statement from the park said that the wreck matches the description of a plane that went missing back in 2011.

The rafters were hiking at Mile 104 of the Colorado River when they came across the wreckage. Park officials have yet to officially identify the plane, but it appears to be the red, home-built RV6 experimental craft flown by Joseph Radford out of Grand Canyon Airport on May 11, 2011, according to National Parks Traveler. A search was carried out across 600 square miles at the time, but the plane couldn’t be located. The AP reports that the wreckage was wedged between two boulders and naturally concealed.

“It was so smashed, so compressed that it was really hard to find an actual skeleton,” John Weisheit, one of the rafters that found the crash, told the AP. “But then we did notice vertebrae in the cockpit.”

The National Transportation Safety Board (NTSB) couldn’t originally determine the cause of the crash, but, as the AP reports, the agency said that Radford could have crashed intentionally. He had recently argued with his wife and told a girlfriend that he planned to kill himself. Radford turned off his radio signal shortly after taking off from the airport in Tusayan.

The remains are with the Coconino County Medical Examiner, but identification could take several months, according to the AP. In the meantime, the NTSB will investigate the cause of the crash.