during the mission 'Guardian Angels', after you've defended diaz, the cutscene plays where the money is stolen by some hatians on sanchez's, here's a video
http://www.youtube.com/watch?v=eo7IPe_gh1Y&t=5mif you listen, the shot that kills the first hatian is a sniper rifle. None of the guards, lance or diaz have a sniper rifle, so who takes the shot?