Things began to unravel at one of the first decompression stops as Ornstein, 33-year-old instructor Derek McNulty, and three other students ascended from a short trip to the murky 275-foot bottom on that dayin May 1998. Investigators believe she mistakenly switched her breathing supply over to an oxygen-rich mixture known to be highly toxic at great depths.
McNulty later told investigators that Ornstein continued ascending with him and three other students until she was just 40 feet shy of the surface. At this point, he said, she signaled to him that she was out of air. He instructed her to switch to another tank and head up another ten feet, then went to help another diver who had entangled himself in a safety line. But Ornstein overshot the 30-foot mark and floated up to a depth of 20 feet. Apparently suffering from the onset of oxygen poisoning, which can cause visual disturbances, nausea, or disorientation, she struggled to cope with her buoyancy equipment, which was later found to have malfunctioned. With the surface just a few feet above her, she lost consciousness.
McNulty told Broward County homicide detectives that he saw a burst of bubbles from Ornstein; then he watched her limp body, saddled with more than 250 pounds of gear, begin to plummet toward the bottom. One of the other students swam down after her, but couldn't catch her. Daniel Mitchell, himself a diving instructor—but only a student on this trip—told investigators that there was no physical way anyone could save Ornstein and still stay alive.
When Ornstein's body was found on the bottom the next day, her face mask was off and her regulator was out of her mouth. One of her tanks still contained breathable gas.