It's really unlikely at this point, although it's not clear whose job it was to check the weapon before it was used.
It should always be the person pulling the trigger.
Send everyone that will be handling firearms on set to a gun safety class prior to filming.
You never trust that a firearm is safe until you do it yourself.
Yeah, I'm not a movie industry expert NOR a gun expert NOR a lawyer. But if someone handed me a gun and and said it's safe to pull the trigger and I did so and killed someone. I have to believe I'm guilty of some sort of crime. Perhaps it would be different if he had a pop-gun and it somehow created a Rube Goldberg like domino effect that caused a ladder to land on someone's head. But a real actual gun that is capable of killing someone is, well, capable of killing someone. There has to be a difference.