Since we know that the reporter is an insurgent, and we know the bodies had been disturbed, there is little reliable physical evidence to back up the insurgents' story. People shot during a battle does not equal execution. People killed in a bomb blast can be shot again after death to create false evidence of an execution.
In an insurgent stronghold, in an event reported by insurgents, with insurgents and their kin as the only witnesses, I would tend to give every benefit of the doubt to the marines.
When insurgents hide among civilians and even family members, it is inevitable that non-combatants will be killed. It is so inevitable that, while any normal human will regret the tragic loss of their lives, it is not even worth an apology.
It all fun and games for the Jihadies util the Marines waste their whole family in the firefight. Even the kids "knew about the bomb" according to one video tape of "survivors" braodcast by CNN. So Iraqis don't want your women and children killed in firefights, don't hide behind them to attack us.