A lot to cover here. There are more unknowns than knowns, that's for sure.
Taking a run at the knowns:
The Venn Diagram of INGO members and Alec Baldwin fan club members is two circles. Nothing wrong with that, just pointing it out. Our middle name is "Gun" and last name is "Owners" after all.
A very young and talented Cinematographer is dead, another crew member seriously wounded.
Multiple sources cite crew treatment and safety concerns. The lack of sleep noted by several caught my attention.
There is a huge difference between a "prop gun" and a "gun used as a prop".
Unknowns:
How did the live round get on the set?
Who loaded the live round into the firearm?
Why was a live round loaded into a firearm on a movie set?
What specific safety protocols were violated (for motion picture producation, not the 4 rules which were obviously violated)?
What were the specific sequence of events prior to the live round being fired?
Words such as "accident", "negligence", "culpability", "criminal behavior", "civil liability" will be applied, but to whom?
I'm curious what they call a "live round" to begin with.
To me a blank cartridge is a live round, it makes the gun go bang.
As opposed to a dummy or inert round.
Both are used in movies.
A cartridge with a primer, powder and a bullet is also a live round.
I don't think any movie would use those.
What kind did they use?