He pulled the trigger, and that was an inherently unsafe activity.
I do believe it was an accident out of stupidity, so it’s still at least manslaughter.
Alec needs to stop saying he didn’t pull the trigger. That is asinine.
I will bet $1000 that he took the gun, gripping the single action revolver with the trigger fully pressed. He then pulled back the hammer expecting it to be cocked and let the hammer go. The hammer struck the primer and the cinematographer suffered a fatal wound.