May your memory never fail you. Because your procedures and fail-safe checkpoints sure can. Complacency was not the root cause here.
See the post above as to why "official" facts are not going to be more informative or authoritative than what those who were there have already stated here and elsewhere. However, has anyone analyzed the bottles remaining in his garage or that were with him on the trip but not dove? With what result? That'd be an "official" fact I think we'd all be interested in learning.
Several of his dive buddies have speculated that, based on the facts known, Carlos had several identical O2 bottles and filled one with air after he'd emptied it on his Doria trip. Unfortunately, he didn't label it as air because he seems to have grabbed an identical-looking bottle that was still full of O2. Even more unfortunately, he didn't analyze the "unlabeled" O2 bottle because he was apparently sure he'd just filled it with air. At a level of unfortunate bordering on unfathomable, he didn't analyze the O2 bottle after being asked to on-site because, again, he remembered filling it with air.
That's not a failure of procedures or fail-safe checkpoints, it's a failure of memory. Relying solely on memory is complacency; ignoring requests to analyze a bottle that you haven't even labeled correctly is past complacency and into intentional conduct that gutted the utility of a fail-safe. You say "presumably diving procedures are supposed to account for human error" without understanding that there's no voluntary procedure that can fix someone who ignores it and others who remind them of it. And we don't do involuntary procedures.
That said, I don't think anyone here is looking down their nose at Carlos because he made a series of unthinkable mistakes that killed him. We all recognize what those mistakes were and our minds boggle that he could have made even one such mistake, much less all of them. But he made them.
And despite our willingness to analyze his mistakes here, we also all are hopefully cognizant of the fact that even after this post-mortem, and even after our resolutions to be more vigilant about checking our own gas and our complacency in general and not make the same mistakes that killed Carlos, some day in the future one of us who knew about the lessons this death had to teach will
still do something just as dumb and get themselves killed. It is, as you say, human nature. We're just trying to avoid falling prey to it ourselves. Most of us will succeed, but not all of us.
