Yuri Lipski's death and its circumstances are relatively well known due to a video now available on Youtube in which his last dive was filmed from a hand-held video camera attached to his forehead.
The dive incident happened at the Blue Hole close to Dahab in Egypt.
While the cause of his death was drowning, the circumstances which ultimately led to his drowning are still unclear, giving rise to rumors of his "mysterious" death.
From the video it is possible to speculate about events immediately preceding his death. Such possibilities include that a rapid descent caused severe nitrogen narcosis which possibly resulted in him blacking out after hitting the bottom at 91.6 meters. Alternatively, a convulsion due to oxygen toxicity in which he lost his regulator and drowned is another possible circumstance leading to his death. It is unclear, however, if his frantic movements towards the end of the video indicate a convulsion or rather were panicked attempts to return to the surface. The video does not clearly show what was happening to Lipski, and ultimately the "mysterious" circumstances surrounding Lipski's death add to the lore and notoriety of the Blue Hole as the "World's Most Dangerous Dive Site."
Further examination of the video/audio brings certain issues to the forefront: Once on the bottom, he blows his BCD which indicates consciousness and an attempt to get back to the surface. Later, his face appears (mask on) on the left side of the video, and he then pushes the camera (and probably the hand to which it was attached) down into the sand in what appears to be an attempt to push himself off the bottom or climb towards the reef wall. Further struggling is evident throughout the remainder of the video, and the sand and sediment which is stirred up obscures the view from the camera lens. The recovery team found his equipment purposely removed from his body, once again indicating a conscious attempt to escape the bottom. The camera going dark is actually a mechanical failure due to the depth or as a result of being dropped during the struggle. The camera snaps a "still shot" but the audio continues to run in the background, a common feature found on many video cameras. A single bottle of air for Yuri's 90-meter dive (assuming he actually intended to dive that deep) would very likely have run out within his ten minute dive, leaving nothing in reserve for decompression stops on the way back up. The dive was beyond his certification level, beyond the capabilities of his equipment, and thus far beyond his own diving abilities. While some believe the circumstances of his death to be mysterious, the only real mystery is whether he drowned after developing nitrogen narcosis, oxygen toxicity, or simply was unable to become positively buoyant after rapidly descending to over 90 meters (295 ft) with an insufficient air supply.
Based on the sounds, there are some hints that could indicate issues with the equipment in the very beginning of his dive:
17:06:13 Up to this moment in the video, all other sounds are normal breathing and environmental; the video shows that Lipski had just passed his dive buddy while descending. At this moment, a sound like "help" is heard, which could be an echo from something breaking or tearing or from a membrane/bladder defect (like air flow through a tight balloon end).
17:06:14 A short, intense air flow is audible, which can either indicate an anomaly in his equipment or a normal BCD inflation. This is the first occurrence of such a sound in the video.
17:06:17 The same intense air flow sound again.
17:06:25 And again.
17:06:40 A sound similar to (possible manual) BCD inflation.
17:07:35 Some time later, the air flow sound again.
This series of sounds could indicate that he was well aware of his negative buoyancy, and tried to establish positive/neutral buoyancy after seeing the slower descent of his buddy.
Regardless of the precise circumstances, the video seem to indicate that his death was a tragic case of an unqualified diver attempting a dive far beyond his abilities and equipment. (Wikipedia)