“You focus on the one thing,” Herbst says. “You don’t focus on the dive anymore. The one thing becomes everything. And I think with Dave it become the body, the body, the body.”

Now Shaw is acting confused. He is working at the torso, instead of the feet. His movements have lost purpose. After more than two and a half minutes of work—and three minutes and 49 seconds on the bottom—Shaw pulls his shears out, fumbling to open them. The plan was for him to cut the dive tanks away as he rolled the bag over Deon. Shaw's breathing rate continues to increase. Suddenly he loses his footing on the sloping bottom. He scrambles back to the body in a cloud of silt. The grunts of effort, hateful little bursts of sound, are painfully frequent.

Shirley and Herbst guess that Shaw's narcosis was then closer to six or seven martinis. "You focus on the one thing. You don't focus on the dive anymore," Herbst says. "The one thing becomes everything. And I think with Dave it became the body, the body, the body."

Still, Shaw keeps checking the time on his dive computer. After five and a half minutes on the bottom, he's aware enough to know he has to leave, but he doesn't get far. The video shows the bottom moving beneath him. Then Shaw's forward progress stops. His errant cave light has apparently snagged the cave line tied to Deon's tanks. Shaw knows he has caught something and turns awkwardly. His breathing starts to sound desperate. He pulls at the cat's cradle of cave line, as if trying to sort it out. Every breath is now a sharp grunt. Shaw struggles to move forward again but is anchored by the weight of Deon's body. The shears are still in his hand, but he never cuts anything. The pace of his breathing keeps accelerating, and there is a tragic, gasping quality to it, so painful to listen to that Herbst and Shirley will no longer watch the video with sound.

Twenty-one minutes into the dive, the sounds finally start to fade. Dave Shaw, with carbon dioxide suffusing his lungs, is starting to pass out. He is dying. It's heartbreaking to watch. A minute later there is no movement.

DON SHIRLEY SURVIVED that day, but he didn't walk away unscathed. He emerged from the recompression chamber at Bushman's, which was pressurized to a depth of 98 feet to shrink the helium bubble in his head, after seven hours, disoriented and barely able to stand. He was so weak that Herbst dragged a mattress over from the police camp so Shirley could sleep right there. Over the next two weeks, he endured ten more chamber sessions, for a total of 27 hours of treatment. It was more than a month before he could think clearly or walk down a crowded street without his perception and balance running haywire. "When I first saw him, I got a hell of a shock," Andre Shirley says. "He could not walk without support, and his thinking patterns had been affected. He would sound sane, but two minutes later he would forget what he'd said."

Shirley has improved with time, but the helium bend left him with permanent damage that has impaired his balance. In May he went diving again for the first time, with Peter Herbst hovering protectively alongside. He closed his eyes, turned somersaults, and with relief discovered that the Big Dive had not taken one of the things he loves most. "A cave is a place where I live," Shirley says.

A week after Shaw died, Gordon Hiles brought the video to a guest house in Pretoria, where Shirley was staying while undergoing recompression treatment at the Eugene Marais Hospital, and Shirley finally watched it. "It was difficult to see, but I really wanted to know firsthand what went on," he says. Later that day, Shirley took the video to the hospital, where he met with Herbst and Dr. Frans Cronje, medical director of Divers Alert Network Southern Africa, who was overseeing Shirley's treatment and assisting with the official accident investigation. They watched the video on a large screen and spent hours poring over every detail.

Shirley was so focused on what he was watching that he started mimicking Shaw's breathing. Then, determined to "see for myself what happened," Shirley volunteered for an unusual experiment. As Cronje carefully observed, Shirley sat with a CO2 monitor in his mouth and headphones on his ears, watching the video one more time. Every time Shaw breathed, Shirley breathed. Eventually Shirley was huffing through 36 shallow, extremely rapid breaths a minute.