That is one of the points I do not understand. What was it in the standards that required him to leave students unattended at the bottom? Even if he was required by his employer to have more than two students, did his employer require him to leave some unattended on the bottom?Why multiply your problem by breaking them again by leaving Sam alone too?
This instructor might as well have been in a resort.
The big difference is visibility. This was a murky lake, not a resort with crystal blue waters. When you know you are descending into murky water, then you know there is a larger likelihood of trouble, and you know you can only see a short distance when in supervision. As I have said several times in the threads on this case, I teach OW students under these conditions, and I will never be alone with more than two under water. Never. I will be close enough to prevent bolting. If I have to go to the surface for any reason and don't have an assistant to leave behind, anyone else goes up with me.
People seem to think that making a decision like that requires one to think like an Einstein. It seems like common sense to me. Not only that, as was shown in a thread on low visibility instruction in the Instructor to Instructor forum a couple years ago, PADI has an instructional film explaining exactly that.
Just to be sure back when that thread was going on, I contacted PADI and asked a series of questions about low visibility instruction, and I got clear answers. It did not take Einstein-like brilliance for me to do that, either.