I can't remember if I said this before... maybe if I did it got lost in the noise of the internet forum diving experts.
If there is a dive fatality, the gas content, amongst other things, has to be properly analysed. This is something only an independent and certified professional Lab can do (or maybe NEDU, if you entirely trust the military...).
Granted that I am 100% sure (my opinion, not fact) that in this case it was human/team error and Carlos unintentionally exposed himself to O2 too deep, we can't know that there was not a small amount of cyanide in his tank (just an example, but if you want to take somebody out a few guys could get together, agree a story, and kill another guy with a cyanide laced tank).
Cyanide would show in an autopsy and this is just a crazy example which comes to mind and not applicable here specifically, but it is for the purpose of making a point which maybe, just maybe, some, but not all, can understand.