There is only one thing we know for certain about Haditha: Something bad happened in the wake of an IED attack on U.S. Marines, resulting in the deaths of some civilians.
The rest is a confused tangle, as MacRanger describes.
The Naval Criminal Investigative Service is investigating this incident. Their job is to untangle this web and get to the facts of the matter. If crimes were committed, they will arrest the suspects, and the military justice system will handle it.
UPDATE: More from Sweetness & Light on this. Again, it is important to let NCIS sort all of this out.