From what I know though, contractors (including those of other companies) have never faced any sort of trial before (at least of 2006) for cases of shooting civilians.
Their effectivenes so far has been due to the fact that they are not restrained as heavily as the military is but with alleged incidents like these (and several possible actual ones before) I think that's going to come to an end.
And like I said, I think this is only the beginning. Once the war in Iraq is over and there isn't going to be a major contract for several years, they are going to turn to dirty contracts to stay alive.