What happened in Haditha?

Unfortunately, I still don't know much more about the incident in Iraq than I did before watching the PBS 'Frontline' program last night. I will go into it more later, but I found it very sketchy, and unclear on many particulars of the various attacks -- on the car, in the three houses. The heralded new footage from the aerial drones shot during the attacks showed nothing really. Little or no mention was made of the fact that nailing down the evidence has proven difficult for prosecutors because of the unwillingness of Iraqis to talk and the rapid burial of bodies. The legal proceedings were very poorly explained. And as for the big picture: Yes, soldiers under unbearable stress will sometimes shoot first and ask questions later. We get it. Now, what really happened?