Alrighty, let’s see what you’ve been up to.
(Which is to say, it is as he has said and as you yourself have concluded - in this case, the person is an accomplice.)
the gunshot would’ve been fired from a pretty high-caliber revolver, which would’ve been pretty loud and, in turn, make it harder to determine where exactly it came from. Krauss was the one to assume Natsuhi was in danger, and most of the other people flocked to the entrance of the VIP room due to the commotion.)
…Meet your old friends, X and Y:
For this to have been possible, it would’ve had to have been done before any of the witnesses showed up to begin with, since Jessica was already on the ground when they arrived. And if that’s the case - is there any point? She still can’t be the one to fire it, as you’ve suggested, given that the person had to have been alive when the gunshot went off. And you’re right back where you started - since by the theories fired this far, Jessica’s already dead and not able to fire the gun, neither Shannon nor Genji can do it.