Thanks to jjhill for adding in your experience. Thanks also for giving this diver all you could. He undoubtedly was given every possible chance he could be given in the circumstances and was in very capable hands.
People talk about failures in the buddy system, but in the right kind of conditions, the most attentive diver can lose track of a buddy. If you are diving in even moderately poor visibility and glance at your gauges at the moment your buddy has a momentary buoyancy issue, you can look around in fear, bewildered at the disappearance of someone who is really only a few feet above you. If the person is having more than a momentary loss of buoyancy, you might never make the connection.
I was once in a group of four divers following another diver in poor visibility. He made an unexpected turn, and poof! he was gone. We held still hoping he would come back. He later said he could hear our bubbles but could not find us.
I agree. Speaking for Waterton overall and not specifically Cameron Bay, even with "good" visibility of 15-20 feet, it can also only take a few misplaced fin kicks near the bottom (from yourself, your buddy, or another diver passing by) to lose
any useful visibility. I don't know how close to the bottom the class itself actually was just prior to the diver being discovered missing/being found, but as jjhill pointed out, the location where the incident occurred/where the weights (removed by the DM) were found was sandy and one that could easily be stirred up, which is typical of Waterton. My buddy and I are always in very close contact and checking in with another and there are times that, if we get silted out by another diver, we can't see each other despite being 1-2 feet from each other. When diving with multiple other divers, despite knowing they are right in front or right behind me, sometimes the best I can hope for is a few blurry shapes or the flash of a lighter coloured tank or fin.
Waterton is a spectacular area, and one of my favourite places to be (for more than diving alone) but it does have its own unique hazards, as does any dive location. This incident was a reminder to me that one should never underestimate the dangers of diving even their "local haunts".
I sincerely doubt we will ever have much more information than has already been provided. It is not a "hot" news story, and there is no mandate on the Alberta Underwater Council or anything to investigate scuba deaths. The only one who really knows what happened is no longer around to tell us, as not even the divers who were there can tell us what happened in those 2 missing minutes.