He turned off the air to suffocate him. This would enforce the theory that he died of suffocation while diving in the ocean.
" Well that clears that up!"
Yes, but that was a large vault - probably with more than enough air for him to survive the week.
Would you like to test that theory?
I have a climate controlled wine cellar.
Yes but if you remember, he wasn't quite dead when he came back from his trip. Casino senior had to finish him off.