Because he knew that Halls was, according to union rules, supposed to hand him the gun and he'd already admitted negligence in following both the rules of his own occupation as an actor (it would be like me, as a teacher, not following the rules of my own union contract as to when to show up for class, for example). He was also ignoring rules that, as a producer/funding source for the film, he was obligated to perform. He was also ignoring rules about which cast and crew had already complained (in emails and texts). Halyna was one of the people who had given permission to her crew to walk out if they didn't feel safe (and they did). She was acting as a sort of manager for the camera crew (which is how I understand her actual employment position).
So one of the two stories Baldwin told is a lie. Or he has memory problems (in which case, he probably ought not to be handed a gun of any sort). It's true that liability/culpability can be spread around here, but I see nothing to completely exonerate Baldwin who, had he done what the union rules required, would have learned to check the chamber himself (it's supposed to be checked three times, which is a tradition for nooses, breakaway props, car stunt equipment and any other potentially lethal action). Checked three times, by three different people, always two people at a time. So Hannah should not have handed anyone a gun or left it on a cart. She should have been present, shown Halls that there were no live bullets (pretty easy to tell, IMO). Both should know what live ammo looks like. Indeed, Hannah said in an interview that she tried to make sure that the chamber behind the hammer was empty when handed over - obviously didn't happen here, unless Baldwin did indeed pull the trigger twice or "fan" the gun). Then Halls gives the gun to Baldwin, with the same protocol (check where the loaded chambers are and making sure it's all blanks).
In this case, there was no script call for ANY blanks or ANY ammo to be used in what they were doing at that point in time (script supervisor is the source, it's in the police interviews). It was not even a run-through, it was a pre run-through blocking exercise.
Further, Hannah left two other guns suitable for blocking exercises and run-through (firing blanks is still dangerous - everyone has to wear ear protection, etc). She left an inoperable (barrel plugged) replica Colt .45 with the weight and heft of the real thing for just the sort of practice Alec was doing. She left a plastic or rubber fake gun (which would have served as a costume item for the scene they were about to film - because it was not yet Alec's big final shoot-out scene).
Halls chose the wrong item. He wisely accepted his plea bargain and probably told the court what happened (I assume he told the truth - he probably admitted he gave the wrong gun to Alec). Alec, however, did not follow the protocol and avoided the training in which he would have freshed his gun handling abilities. He had just earlier bragged (on camera) that he was "expert" in all kinds of cinematic abilities, including prop gun handling. He then showed that he was not.
They were all in a hurry, Alec was mad about the camera crew walk-out (IMO) and all of this should rightfully come up at trial. So far as I can tell, the GJ did not hear from any of the cast/crew witnesses (but there are many). They heard summaries of what those people had to say, and other evidence, conveyed by LE at the GJ proceedings (that's judging from what we can see in the pleadings and research on the internet).
IMO.
chicago.suntimes.com
abcnews.go.com
www.cdc.gov
www.forbes.com
jec.unm.edu
www.nytimes.com
