We were there and i had a chance to talk to this pair before their last dive and after...
The fellow who died was a younger guy, very quite per my account and did not talk much, and in wet suit.
His surviving buddy was in dry suit. remember that point.
Per my account we started gearing up after they came out of a first dive and it probably took us 30 min to get in the water.
There after we had 110min dive and when we surfaced on SMB rescue jet ski was waiting for us saying diver was missing for 30 minutes or so.
So it looks like they had about an hour surface time, hardly enough to get warm in wet suit.
That day vis was very nice 40ft or so in 60ft of water., so easy to get carried away with scenery.
I've shortly talked to surviving buddy his word were "we were in 50ft of water, he (deceased) started going down out of air on a stop, i donated , we surfaced, i could not hold him up, it all went so fast" also he mentioned it was their 3rd or so dive together and that he (deceased) had about 15 dives.
So here is my take.
Set up:
1. Remember myself first few dives im scared and checking everything every minute, after about 10 or so , till first problem i was invincible having
145 ft dive #11 in my book, came up with 200psi that day.
2. Wet suit on second dive in 50 degree water will make you use more gas, so hard for guy in dry suit to judge your consumption.
3. No long hose makes it hard to donate and requires awkward position, try for once donate AIR2 or similar
4. dissimilar gear requires clear brains to think , which may not be possible under panic, set in #3, when you being pulled down.
Outcomes.
1. Very sad and preventable accident
2. Deceased was responsible for his own gas no question there. As a team they should plan that requirement. But ultimately it is my buddy' responsibility for him and for me to check his own SPG and make me aware of problems.
3. Surviving buddy did what he could in this situation, sure we could argue what he could of done, but he did not and this is the end of it., he will live with this memory for all his life, i would not want this.
4. As an alternative, rescue attempt of OOA diver by unprepared but willing buddy more likely result in 2 victims. i recall we had it few years back.