Assuming the sniper is on foot, the sniper may walk miles from the site when he calls in for a pickup.
There's a lot of endurance and concentration here so I'm guessing perhaps different snipers with the gun being passed in a relay type scenario.
Sac
This is an interesting scenario. If we don't know who shot whom, does that make it easier or more difficult to charge/ prosecute them?
Yes, in the opposite direction from the victim.