Nitrogen Asphyxiations.
Strap the condemned down.
fix a brain wave detector.
medical breathing mask attached to a nitrogen supply
flow 1.1 atmosphere 99% nitrogen.
Condemned goes to sleep
make sure the room is well ventilated
wait till brain waves have been flat for 5 min.
Declare dead.
No messy body parts or blood splatter.
No possible missed veins
No drug shortages
Helium asphyxiation makes for much funnier last words.