Is it possible the trigger was just a really sensitive hair trigger and a slight shake could cause it to pull back?
You have two perform two actions to fire a single action revolver. '
- You have to pull the hammer back (this operation usually performed with the thumb).
- You have to depress the trigger (this operation typically conducted with the index finger).
Baldwin's claim that the gun just went off is implausible because an antique gun isn't like a Glock with a bullet in the chamber.
If as you suggest, he cocked the hammer, then he made the gun ready to fire. Cocking the hammer on an old revolver is basically saying, "I'm ready to rock and roll!" because these guns have light single-action triggers. Thus, cocking the hammer and then pointing the gun at Halyna Hutchins is still gross negligence, at best.
And if a mere shake did make it go off, then the gun would have had to have been mechanically unsound (e.g., a dangerously worn sear). However, it is rather easy to confirm the condition of a firearm by having it inspected by a gunsmith. It is unlikely that the gun was damaged in this manner. If it is, however, damaged in this manner, this is a fact which can be easily settled.
And if Baldwin keeps blaming the gun, don't be surprised if the gun's condition is inspected at trial. The most likely scenario is that he cocked the hammer and depressed the trigger while pointing the gun at Halyna Hutchins.
Caveats:
A period SAA revolver does not have a safety transfer bar. The firing pin rests adjacent to the primer. It is, therefore, possible hit an old revolver with a block of wood or hammer and make it go off by causing the firing pin to connect with the primer. This is why cowboys only loaded 5 bullets into these guns (they call them six shooters, but they only loaded five). For carry, they would have the hammer rest on an empty chamber to prevent an accidental discharge.
You can partially pull back the hammer over a loaded chamber and release it and have it strike the primer with enough force to cause a round to go off. And you can do this without depressing the trigger, but this is unlikely, because when you pull back the trigger it sets to half-cock, before it goes to being fully cocked. My guess is that he was depressing the trigger the whole time (without realizing it) and that when he released the hammer he got a surprise "bang!"
Yes, it is possible that Baldwin could have negligently pointed the gun at Halyna Hutchins without pulling the trigger. However, the strong probability is that he cocked the hammer and pulled the trigger.