While this incident was indeed a tragedy, any person should not be handed a weapon and told it is unloaded. It is the person who is handed the weapon to insure that it is, in fact, not loaded. You should never, ever, accept a weapon without verifying it is, in fact, not loaded.
If you do not know how to check a weapon to be sure it is not loaded, you should not handle any weapon at all.
In my opinion, Alec Baldwin was responsible for checking the weapon to be sure it was not loaded and no one else.