It’s difficult for people in the kill box to determine the direction via the sound of the report, because at that range, there is also the crack of the sonic boom of the bullet that is heard before the report of the rifle. Add to this any other buildings that are reflective surfaces for the sound, and it is incredibly difficult to determine via audio cues alone.

If someone saw a muzzle flash, that would hold a lot more credibility to the actual location of the shooter.