If the Marines came through the doors with guns blazing, it's not because they wanted to kill innocent Iraqi citizens, it's because they thought there were NOT innocent Iraqis there, only terrorists who had killed one of their own with an IED, and were waiting to kill the rest of them.
That's my understanding of the ROE. I think Gen Hagee flew out to tell them to be more cautous about the execution of those ROEs.
"It is criminal that the terrorists had left the people in those homes to fend for themselves as they ran away to save their own sorry hides."
The terrorists operate by threat and intimidation of the townfolk. The townfolk may be sympathetic, but most of them don't activly engage in the violent action, just sneaky stuff. In this case those in the first house were used to set off the bomb. See 9y/o Eman Walid's comment(CNN).
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Marines don't go through doors with guns blazing these days. They're trained in CQB (close quarters battle), good at avoiding civilian casualties, and instructed not to fire at anyone who's not an armed threat.
If the Marine convoy leader filed a report saying that 15 Iraqi civilians died in a blast, when he knows that only one of his guys died, it looks very suspicious. It would be a hard sell to say that they killed 15 people on accident, given their level of training, but it'll be a lot harder now that it looks like he was covering something up.
A few civilian deaths is very understandable in any squad level fight; it's unfortunate, but it happens. 15 to 25 in a lightly populated residential area sounds, at best, like serious negligence. If that was the case, and that's why he tried to cover it up, the plan didn't work.