Is it perfectly clear that it was Iraqis who did this terrible thing? I thought that Al Quaeda were outsiders.

There is no justification for this act of barbarism. But is it a reaction that needs to be explained? People don't do hideous things like this without some kind of agenda that needs to be understood. To dismiss this horrible act as being that of a sub-human or evil person is missing the point and begging the question.
Why? Don't we need to be asking this? This was not an act by a hungry tiger.

How did this branch of psuedo-Islam become so distorted?

For that matter, why are there madrasas popping up all over the place?

Is this to be interpreted as a "holy war"? Who are the real combatants, here?

Frank