Silly questions don't demand intelligent answers. "Most secure city"?? What city is so secure as you suppose this one is? That is silly. Cities are not "secure".
What if an AQ agent could do this? Well... of course they could. It would be easy for anyone, or a big group, to go on a rampage and say... shoot up shopping malls all over the country. It would paralyze the country and there is no way to stop it.
So what?