Shooting the Italian Hostage

Well, by now everyone has heard about the incident in which American troops fired on the car carrying the recently freed Italian hostage. (If not, read it here.) I know there will be an investigation; I know that we want the Americans to have, in fact, acted properly; I know that the Left will be accused of hating America if they criticize any facet of the U.S. military over this incident.

Here's my question: the story told by Giuliana Sgrena, the freed hostage, contradicts the story told by American soldiers. What reason would we have for believing that she is lying? Granted, there are multiple sides to every story, and we understand that the truth probably lies somewhere in the middle of all of them. We know that American soldiers for the greatest part perform admirably and honorably; we also know that honest mistakes happen in war, and that unfortunately every barrel has a bad apple or two.

I'd like to hear your comments on this. I'm hoping for a discussion that goes beyond "the U.S. is always right!" or "War is always evil!" Sgrena is the one who was shot and whose rescuer died on top of her, saving her life. What good reasons do I have for believing, or not, her story?