In handling any firearm, proper care is to verify the status of it yourself even when you watch someone else do it in front of you. That is not a responsibility that can be outsourced or delegated. Actors are suppose to be trained the basics of firearm safety for the gun(s) they need to handle for the movie.
not on a movie set.
no actor is responsible for verifying the firing condition of any weapon.
no matter what safety or handling training they've received.
negligent: failing to exercise the care expected of a reasonably prudent person in like circumstances.
no actor is expected to know or verify the firing condition of any weapon on set. It's really that simple.
It was not Alec Baldwin's responsibility, in any way, to check if the firearm was loaded with live rounds, blanks, or dummies.
Never.