Not exactly sure why everyone is intent on ripping you a new one on here...I understand what you're saying in principle.
While the token sympathy in a large portion of the threads posted in here are fantastic - I'd argue its no more productive to boo hoo and wee wee wee all the way home any more than it is to make reasonable observations on what could have possibly led to the fatal mistake.
It sounds like the crew did just about everything they could - but I personally still hold them accountable for anything that happens on their shift. By and large, not being critical of the situation, regardless of how much information you have, is probably better than saying nothing at all and waiting 3 weeks, or 3 months before all the information is availible. Watching bubbles is a passive activity, but I'm suprised not one person on that crew was investigative enough to engage a more active role in ensuring the divers safety. I seem to have come accross a fatal trend of passive observance - mirrored in many of the fatal and non-fatal accidents listed on these boards.