“Yeah, but they’re hyperventilating for O2”
I Understand, but procedural protocols would be in place. For example:
A pre-op sedative, some oxygen in a mask, switch the mix to nitrous oxide (laughing gas) to deepen the unconsciousness, then introduce the nitrogen. Monitor the vitals for prescribed time and note the time the murderer expires.
I think Oklahoma has already used nitrogen.
Firing squads might be quick. But the bio-hazard component of the procedure introduces unnecessary risks.