Now this I can go with. Blow back.
Did the authorities have prior knowledge? Likely? To me this seems to be more like damage control. They weren't able to unfoil a terrorist plot in time to protect the public. So they flex some muscle in pursuit of one kid to show the country "we are tough on terrorists". Incompatance is most likely the culprit here. Somebody didn't do their job. They should have called the event off. But that event is a big money maker for the city. Oops.