yes, but covering it up also prevents any political impetus to have law enforcement do anything about rooting this out domestically. the beauracratic mentality says "don't worry about it, nothing happened, no one knows, just move along".
if this was a terror attack, that tells us alot about how poorly domestic law enforcement agencies are at sweeping this out from inside this country.
I wouldn't paint with such a broad brush. Consider that we have a never-ending stream of potential Islamists planting themselves in universities nationwide, and most of those universities don't want to endanger their cash cows (full tuition, paid in advance) by reporting dropouts or suspicious behavior to the feds. Meanwhile, Foggy Bottom is still allowing European Muslims to enter on the visa-waiver program.
It's much like playing whack-a-mole, with the ACLU, academia and a wide range of powerful financial, political and/or leftist interests on the moles' side.