Le Gallou’s four fellow jumpers hoped their friend had pulled his parachute safely above the plateau. The whole flight path is not visible from either the valley or the exit point, and it was possible, they believed, that he could have landed unseen. After hiking for a while to get better phone reception, they tried to call Le Gallou. Nothing. Brennan remembers the group opening beers to celebrate their successful jumps while they waited for news.

Image Le Gallou and Benoît Paquet in Verdon Gorge in France in 1998. Credit... Photograph from Benoît Paquet

“Just after like the first sip of beer maybe, we heard a helicopter coming over,” Brennan recalled. “And the helicopters never fly over there unless they’re doing a rescue or something. . . . The worst sound I’ve ever heard in my life was the sound of that helicopter coming.”

A passing hiker saw the fallen Le Gallou and called mountain rescue. Le Gallou had hit the plateau and died on impact, his canopy stretched out behind him. In the days that followed, three of the jumpers posted accounts on base Web sites, detailing what they thought went wrong with Le Gallou’s last flight. Frat wrote that “for reasons we can only speculate, he was unable to outfly the plateau.”

For Joumana Seif, Le Gallou’s former girlfriend, however, the accident could not be dismissed so easily. Seif, an elegant, 36-year-old orthodontist of French and Lebanese origin, lives in Geneva. She met Le Gallou through base jumping, and beginning in 2001, they had what she describes as an “intense” relationship. They split up in 2005 but remained close friends. When Le Gallou died, Seif organized several events in his memory, including a cremation in Grenoble, a Catholic Mass in Paris and a base-jumping memorial at his favorite spot at Cirque d’Archiane, in the Alps.

I spent two days with Seif in Paris last fall. As we talked about Le Gallou — Seif often pausing as she wept — she told me that two things bothered her about the accident. The first centered on the question of character. Le Gallou, she said, was a conservative base jumper. (This may appear a contradiction in terms, but as many of his friends confirmed recently, Le Gallou rarely pressed beyond his limits. Mavericks do not survive 18 years in a sport like base.) It seemed implausible to Seif that Le Gallou would have tried a risky line on his flight from Obiou. If he’d lost good finesse, she thinks he would have pulled above the plateau and lived to jump another day. To her, there was only one root cause for the accident: equipment trouble. The fact that his parachute was deployed when he crashed indicated some kind of delay in finding the handle for his pilot chute, the small canopy that precedes the larger parachute. (Failing to find the chute’s handle is known as a No Pull Find.) Once Le Gallou realized he was in trouble, Seif believes he lost precious fractions of seconds trying to deploy his pilot chute. By the time he did, it was too late.

Her second concern was Le Gallou’s helmet camera. It was his habit to record jumps. On the day he died, he wore a ContourHD camera attached to a rugby helmet. Grieving and searching for answers, Seif hunted feverishly for the device. But after the accident, the Contour camera was nowhere to be found. It was not among the personal effects collected by the police. Seif says she searched the crash site six times with a metal detector but found nothing.

None of Le Gallou’s fellow jumpers had an explanation for what happened to the device. Seif recalled that when she asked about the camera some days after the crash, one of the jumpers told her it was useless to look for it. “‘Maybe it’s in a million pieces,” he said. “Maybe a marmot took it.’ ”