Federal investigators found remains amid the wreckage of missing adventurer Steve Fossett's airplane in the mountains of eastern California, but there are conflicting reports as to whether the bone fragments are human.

Search teams planned to hike back out to the site Friday to scour the steep flank for more traces of the lost aviator.

The National Transportation Safety Board (NTSB) said searchers found enough at the crash site to provide coroners with DNA. The bone was discovered in a field of debris that stretched 400 feet long and 150 feet wide in a steep section of the mountain range.

Click here for photos | Click here for video

"We found human remains, but there's very little. Given the length of time the wreckage has been out there, it's not surprising there's not very much," National Transportation Safety Board acting Chairman Mark Rosenker said late Thursday. "I'm not going to elaborate on what it is."

But Madera County Sheriff John Anderson later seemed to contradict Rosenker.

"We don't know if it's human. It certainly could be," Anderson said. "I refuse to speculate."

He described the finding by one of his lieutenants as an oblong piece of bone, measuring 2 by 1 1/2 inches.

He said it would be sent to a California Department of Justice lab for testing.

Asked about the sheriff's assessment of the physical evidence, NTSB spokesman Terry Williams reaffirmed Rosenker's earlier statement.

"We stick by that. It's human remains," said Williams, who declined to say how the NTSB had arrived at that conclusion.

The 63-year-old intrepid balloonist was scouting locations for an attempt to break the land speed record in a rocket-propelled car when he vanished.

"I hope now to be able to bring to closure a very painful chapter in my life," his widow, Peggy, said in a statement. "I prefer to think about Steve's life rather than his death and celebrate his many extraordinary accomplishments."

Earlier Thursday Anderson said searchers "found enough wreckage to determine that it was in fact the aircraft" Fossett was flying solo when he disappeared last September. Fossett apparently plowed head-on into a mountainside.

"The crash looked to be so severe that I doubt if someone would have walked away from it," said the sheriff during a Thursday news conference before the body parts were found.

The engine was lying about 300 feet from the wings and the fuselage, which disintegrated on impact.

"It was a hard-impact crash, and he would've died instantly," said Jeff Page, emergency management coordinator for Lyon County, Nev., who assisted the search.

Fossett's mysterious disappearance prompted a massive search that covered 20,000 square miles, cost millions of dollars — and sparked rumors that he faked his own death because he was buried in debt.

Crews confirmed about 11 p.m. Wednesday that the tail number matched the one on the single-engine Bellanca Fossett flew, according to Anderson.

Meanwhile, California National Guard troops also were scheduled to head to the rugged spot in the Inyo National Forest where searchers located the wreckage. They planned to airlift out the surviving portions of the plane in Blackhawk helicopters so they could be reassembled and examined at a nearby hangar.

The discovery of the decimated fixed-wing plane came days after a local hiker stumbled upon some of Fossett's personal effects — including his pilot's license and FAA cards.

Investigators said animals might have dragged the IDs from the wreckage while picking over Fossett's remains.

Anderson said the plane was found about a quarter-mile from where the items turned up. In total, about 50 searches were planned in the coming days, according to the sheriff.

The wreckage was located at an elevation of 9,700 feet in the Sierra Nevada Mountains in the Mammoth Lakes, Calif., area, the NTSB said.

Fossett — who made international headlines with a daring round-the-world balloon trek — was flying alone when he vanished Sept. 3, 2007 on what was supposed to be a routine local flight from Barron Hilton's private airstrip in Nevada and back. The plane was borrowed from the hotel magnate, and the flight was only supposed to last a few hours.

For a while, many of Fossett's friends held out hope he survived, given his many close scrapes with death over the years. A judge declared him legally dead in February.

In August, an attorney for Fossett's widow pleaded for an end to speculation circulating on the Internet that the millionaire pilot may have faked his own death, possibly because he was heavily in debt.

The area where the remnants of the plane were found, situated about 65 miles from Hilton's ranch, had been flown over 19 times by the California Civil Air Patrol during the initial search, Anderson said. But it had not been considered a likely place to find the plane, given what was known about sightings of Fossett's plane, his travel plans and the amount of fuel he had.

Lt. Col. Ronald Butts, a pilot who coordinated the Civil Air Patrol search effort, said gusty conditions along the mountains' upper elevations hampered the early efforts to search by air, as did the small amount of debris that remained after the plane crashed.

"Everything we could have done was done," Butts said.

As for what might have caused the wreck, Mono County, Calif., Undersheriff Ralph Obenberger said there were large storm clouds over the peaks around Mammoth Lakes on the day of the crash.

Fossett made a fortune in the Chicago commodities market and gained worldwide fame for setting records in high-tech balloons, gliders, jets and boats. In 2002, he became the first person to circle the world solo in a balloon.

The Associated Press contributed to this report.