The comment about it not necessarily coming from directly in front of them made me scratch my head a bit. I imagined that if someone was standing between you and the screen you would notice. Or reversely, if you're in the back rows, you may notice someone turning around with a gun? So I am liable ot also think of stray bullet from the outside.

Or, another theory....time travelers come back to stop a future war.

But in all seriousness, this s terrible. Rip kiddo.