as sergeant joshua hedanimi reports. >> a somber moment for the platoon.ect for the guys. it hit us hard. >> dan south the only one in the humvee to survive the attack. >> i smoked the guy that did it when it happened. other than that you never know who did it, you don't know what happened to them. as far as you know they got away with it scot-free. >> reporter: and not just get away with. an abc news investigation found that the two terrorists, alwan and hamadi, were able to get through a fluid u.s. system of background checks and end up in bowlingling green. one living in this public housing apartment on public assistance, put under 24-hour surveillance by fbi agent dick glen and others. >> when we realized we had a man here with american soldiers' blood on his hands, it took it to a whole new level for us. >> reporter: the other iraqi lived in this residence near the high school. >> it's scary. >> reporter: and as the fbi would learn in the course of its undercover operation, the two iraqis were intent on killing even more americans. >> these two indivi