Knowing with "relative certainty" is not knowing at all. It's like being partly pregnant.
No it's nothing at all like that.
You just don't want to accept the reality.
Even a full autopsy will not reveal the specific oxygen overload of an Oxtox hit- dissipation/diffusion would prevent such analysis.
The ONLY thing you use to cling to in your misleading article that rationalizes (to you) that there is some "unknown" is that a police forensic lab did not measure the bottle's oxygen content.
The question is WHY WOULD THEY NEED TO? At the scene - a dive instructor- with years of cave experience produced an oxygen analyzer. In front of police and others- the gas was tested. It showed +\- 98% oxygen. The bottle was marked OXYGEN. In order to calibrate the analyzer before the measurement it would have to be "zeroed" to air (21%). So there is no reason that anyone else would need to be performing the analysis. The bottle markings matched the contents. Police would not need to farm out forensic work to reconfirm something in a non criminal investigation. The death was not suspicious, it was -as the English like to say- misadventure.
Because you desperately cling to the incorrect notion police should have done something more does not make it any less real that the sole and rationally undeniable cause of death was operator error.
Absent some evidence of foul play or someone else's contribution - police do not engage in fishing expeditions when a cause of death is patently obvious. When they come upon a man with a gunshot wound to his head, consistent with self infliction- powder burns on his dominant hand, a loaded and recently discharged firearm in it, sitting in a room locked from the inside with a suicide note written in the handwriting of the deceased- and having had witnesses describe the recent behavior of the deceased as suicidal.... Absent any other facts supporting a different conclusion- it's ruled a suicide. Could it be an elaborately framed murder? Yes. Likely, no. Going to be treated as such forensically? No. If the police don't have anything to suggest foul play there won't be a substantial forensic inquiry.
Similarly- in this case- we have:
1) a clearly marked oxygen tank
2) a test confirming that content immediately after the incident by a trained professional in front of witnesses that the content of such tank matches the description on the tank
3) numerous witnesses who said they tried to get the deceased to analyze the contents before the dive because of the tanks markings
4) the deceased's refusal to do so and statement he knew the contents were air
5) a seizure at depth -consistent with oxygen toxicity -while using that very same oxygen labeled tank
6) a similar appearing bottle also marked oxygen not used by the deceased during this dive but in his supplies from his Doria trip
Ockham's Razor applies.
Pregnant is Pregnant.