After analyzing high-definition video, forensic imaging specialist Jeff Glickman even concluded the odds were very high some pieces - resembling a tire, a strut and a fender - came from a plane like Earhart's. He ruled out wreckage from an old shipwreck up the beach.
But no pieces were retrieved, only images, and where was the bulk of the wreckage? The engine? The girderlike main beam? Pieces of wings, or the tail section?
"I don't see anything in the data we collected so far that says, 'Ho, there it is!' " said Gillespie, who'll be speaking about his quest next Thursday at Portabello's Restaurant in Kennett Square. "I see some things that might be man-made objects, that could be airplane parts."
On the way back to Hawaii, though, Gillespie's team confirmed an intriguing insight: An inflated tire can make landing gear float.
That would explain how an old photograph may have led searchers astray.
"I think it's entirely possible we took a wrong turn and made a bad assumption," Gillespie said.
The photo was shot in 1937, three months after Earhart crashed, but not until Glickman closely examined the negative a couple of years ago did anyone notice was could be landing gear sticking out of the water off Nikumaroro's beach.
That photo inspired Hillary Clinton to hold a news conference in March at the state department, endorsing last year's expedition.
The assumption was that the object marked the best place to look - around that reef and in the depths sloping away below.
But the landing gear may have drifted away from the wreckage, Gillespie now suspects.
"If it floated there, where did it float from?" he wonders.
Accounting for currents, a likely spot for the main wreckage is just 150 yards to the north.
"We were simply looking in the wrong place," he said.
He's not worried about some Titanic director James Cameron or some publicity-seeking adventurer beating him to the punch, because TIGHAR has a signed deal with the Republic of Kiribati to be its exclusive agent for retrieving Earth artifacts.
If only the $2 million expedition had more time - or was able to operate more efficiently, it might have gotten to that area, since it was included in the original plan. Equipment troubles, however, shortened the search.
"We didn't have nearly as much time as we planned, and we didn't have the right equipment, and the equipment we had didn't function well," Gillespie said.
The next step seems obvious. Rush back to Nikumaroro with better gear, cover a larger area, including the suspected spot, and retrieve everything possible. Find the plane, case closed.
Not so fast, said Gillespie.
After 10 trips to the island since 1989, he's quite familiar with evidence that teases and promises and fits a working theory but ultimately falls short.
According to a 1940 report, 13 bones were found on the Nikumaroro and examined by a physician, who concluded they belonged to a man. TIGHAR had a forensic anthropologist recheck the recorded measurements, and she concluded the bones belonged to a 5-foot-7 woman of European descent - a description that fits Earhart.
But no one knows what happened to the bones.
Bone fragments found by TIGHAR on the island in 2010 raised hopes of DNA confirmation, but labs have failed to find sufficient genetic material.
A shard of a cosmetics jar matches an Earhart-era freckle cream, and the pilot had freckles, but so far nobody's found proof she used that brand.
Other clues found during expeditions: a woman's shoe, a sextant box, a zipper piece, a broken pocket knife, a chunk of rouge, all consistent with Earhart and her belongings.
But nothing irrefutable turned up, like an engraved watch. Or an easily identified belt buckle.
Gillespie, 65, hopes to get things right next time. End the 75-year-old mystery once and for all.
So don't expect a follow-up expedition this year. And don't expect plans for one next year to be publicized until he and his fellow recovery enthusiasts have had time to painstakingly rescrutinize a lot of the evidence gathered so far.
"Before I can go to the public with a fund-raising campaign, we have to have something specific," Gillespie said.
"I want to take a really hard look at the airplane piece we recovered from an abandoned village," he said. The rivet pattern seems to be off by a quarter-inch, but maybe the part was replaced and a repair order could match it to the Electra.
For some observers, the preponderance of evidence means the mystery is already solved.
Found objects, for example, aren't the only clues. In 1937, many people reported picking up transmissions from Earhart after she disappeared, supporting the idea she landed safely somewhere and become a castaway.
A Florida girl took notes, detailing how Earhart identified herself and repeated something that sounded like "New York City."
A freighter called the Norwich City was abandoned on the beach at Nikumaroro in 1929.
If Earhart was there, she couldn't miss it.
Still, Gillespie wants to remove all doubt.
"I've learned to be pretty tough about this stuff," he said.
"Science isn't a steady upward curve. The important thing is to persevere. You do make progress but it's always a step back for every two steps forward."
For more about TIGHAR and the Earhart search, go to www.tighar.org.
Contact staff writer Peter Mucha at 215-854-4342 or firstname.lastname@example.org.