Sooo, They know them

"Give me one good reason why they don’t arrest them if they are serious on fighting insurgency in Iraq and stopping the killing of innocent Iraqis and American soldiers???.

Pentagon: US knows of 10 leaders in Iraq’s insurgency"

Bagdad Dweller

Maybe they are trying to work with them to bring them in to the mainstream. Maybe they figure that if they can work with them that in the end it will save many more lives. Just maybe with their participation in the process the new democratic Iraq as a whole will have a better chance at success.