I think at some point you have to accept Carlos took a bottle filled with poison diving. If you can allow this to be a human factors accident, it becomes very clear what happened and who is ultimately responsible.
Your requirement for a CSI inquiry would be quite relevant if another party had motive and secretly swapped his tanks, or refilled his gas after he analyzed them in an effort to purposefully kill him. Sadly, the tanks were easily traced back to the prior dive on the Andrea Doria. Carlos failed in his responsibilty as a diver, and the best you could hope for in a trial is assignment of blame by percentage. There are a lot of people who might assign that blame at or near 100% to Carlos as he was soley responsible for checking that gas. Using witness statements - he didn't do it.
Let's assume the evidence that is intact, on-site expert statements, on-site eye witnesses, and immediate on-site gas analysis are all flat wrong. In other words, let's assume all the forensic evidence is gone. We're left with the Medical Examiner's report, and we learn from that a healthy adult male died from drowning. We trace the gear back and discover it was filled by Carlos for another dive and repurposed. We would discover that Carlos did not analyze the gas after filling the tank, and we would probably learn the gas was not marked consistent with the conventions (name, fill date, etc.) We would also learn that Carlos had physical possession of that gas, and transported it to Florida where it remained in his possession until the time of use. Skip everything that happend on the dive, skip the post gas analysis, skip the dive team statements, skip the expert cave instructor's statement, skip the on-site gas analysis. Fast forward to the ME's letter of opinion on the drowning.
Seems like Carlos didn't play by the rules long before standing on the shores at Ghilcrest County, FL and the accident had begun weeks or months before. It was imperative he break the accident chain by taking :30 seconds and analyzing the gas. But it's clear he didn't take half a minute and check that cylinder and he paid for it dearly.
A much more interesting article might have looked at one of the 5-Dangerous Attitudes of pilots. Get-There-Itis comes to mind and has killed many a pilot. The reward of getting things moving quickly overcomes the mundane safety items that seem unnecessary, but checklists and procedures are there to stop bad human behavior - to break the accident chain. In this case, had Carlos followed the rules of a recreational Enriched Air Diver, he would have rejoined his family at Disney World. Afterall, the Medical Examiner seems to think so...