According to the Medical Examiners report, the deaths were a simple out of air situation that went badly.
James and Carla were spearfishing at 107 fsw.
Neither James nor Carla had any medical conditions that contributed to their deaths according to the ME's report. Both their cylinders were found empty but otherwise functioning normally and they were diving with 30%.
According to the video which the ME watched and cited in his report, Carla ran out of gas first and swam to James with her 2nd stage regulator out of her mouth, signaling that she needed air. James donated his primary 2nd stage, which Carla put into her mouth upside down, causing the regulator to flood. Carla inhaled sea water, began vomiting, and became unresponsive moments later.
James attempted to swim them both to the surface, but he had to release Carla. James ran out of gas shortly thereafter and both sank to the bottom. The rescue diver found both bodies 10 feet apart, in 100 fsw. Neither had their regulators in their mouths when they were found. The ME stated the rescue diver "unclipped their buoyancy control devices and attached equipment and surfaced with both bodies", so I'm assuming neither diver ditched their weights for the attempted swim to the surface.
The ME listed the cause of death as "Drowning while scuba diving" and the manner of death was "accident".
I myself have become quite complacent as DiverDownD3 stated. I've been pretty lazy about bringing my pony. I've left in on the boat the last 3 or 4 trips. I've also gotten into the habit of returning to the boat sometimes with as little as 50 PSI remaining in my cylinder. This was a wake up call for me. I'm going to change my ways.
James and Carla were close friends and this information is posted with the permission of the deceased's mother. Hopefully we can all take something away from this incident that will make us safer and better divers. I know I have. Up until now, a dive fatality is just something I've read about online or in scuba magazines.