Some kid or kids or a group of disgruntled people, mad at whatever might have decided to take it out on tourists.
Or, yes , a dry run by a more organized faction .
Doesn't have to be US trained , Bin Laden lead ( allegedly) " Al Qaeda" to be terrorists .
I'd like to say there are plenty of Christian nutjobs out there ( GW Busch) declaring "Crusade" against Muslims.
It is the fanatics of all religions that are the enemy, not just Islam