One thing that I think will come out at trial is the the armorer (working for the Property Master) was an apprentice or newly trained young woman. As Producer and/or in-charge on the set, Baldwin had previously dismissed her from her duties as he disliked her input. She was not involved in the fatal encounter.
My suspicion is that he was allowing firearm extracurricular activities and she was upset. A live round from staff horseplay usage was left in the weapon and bone head Baldwin had the trigger depressed as he was making out his acting.
Her job was to prevent any fatal encounter. She was personally responsible for controlling all weapons at all times, as well as loading and unloading them. She did not do that.
If Baldwin prevented her from doing that job, she should have immediately resigned and walked off the set. She stayed and allowed bad behavior to continue. Other crew members did resign and walk off the set that very morning of the incident, citing repeated violations of safety protocols as one of the reasons.
She was young and stupid, ignoring safety protocols in an inherently dangerous situation. That put her in first position for the criminal negligence that led to a homicide. The Assistant Director was cowardly and stupid. He had no training or experience as a Weapons Handler and should never have touched any firearms on that set. The Armorer should not have permitted him to do so. Handing an unchecked weapon to an Actor puts him in second position for criminal negligence.
Actors are assumed to have the ability of trained chimpanzees and are never supposed to handle a live firearm on any set. Nor are they allowed to dictate terms to the Armorer or Weapons Handler. Baldwin's main defense ("the gun fired itself") is complete bullshit, but his secondary defense ("they told me it was a cold weapon") has some merit. That is the way the movie system is supposed to work.
Except that Baldwin was a Producer as well as an Actor and had a responsibility to see that standard safety protocols were observed and enforced. He did not do that job.