There is no way to prove or disprove this. There were numerous witnesses to the shooting event yes.
The fact of the matter is that O'Sensei died from complications caused by liver cancer at the ripe old age of 86, and not from gun-shot wounds at some earlier date.
Eight witnesses at the event saw O'Sensei survive without a scratch. It may be hard to believe, but I have so far seen no evidence to the contrary.
I might add that there are many Americans that believe the moon-walk was staged on a movie set and that it was a conspiracy to make the Russians believe that the US was actually technologically more advanced than the Soviet Union. Once again, show me the evidence, and I'll believe it.
As the result of a law suit, a lot of top secret information about Area 51 has become a part of the public record. After seeing this evidence, I now have a more clear idea about Area 51.
Facts, evidence, and quality sources unravel lies and reveal the truth. If you've got something to say, back it up. If you can't back it up, it's a meaningless waste of words.