Anyone expecting the local police forces to catch terrorists and such is bound to be terribly disappointed. Local forces, meaning township, city, county, and metropolitan forces, are almost without exception completely unsuited for seeking out the sort of people who would conspire to and succeed in terrorist activity. They have neither the staff, the funding, the training, nor the time. They do well to keep traffic under control, and deal with "normal" criminal activity. They just don't. I'm no fan of the Federal government by any stretch, but in order to deal with real terrorism, be it homegrown or imported, you're going to have to have the feds. Take it from a formal local law enforcement officer, less than 1% of the local agencies have a prayer, anything they hit on will be pure luck and chance. Hell, a lot of state agencies would have trouble. Even when you DO have time and resources to devote to a task like that, you still need to get lucky and get a break, regardless of how good and how smart you are.
And yes, you'll also end up busting idiots and morons who have no idea what they are doing in the process of actually bagging terrorists and stopping their plans. Same thing happens with every other law enforcement task outside of traffic. Working on a drug task force? You'll no doubt bust at least a couple crews of total incompetent fools and wannabes making illfated attempts to move a bag of pot on your way to catching some one with five bales of pot hidden behind an access panel in a tractor trailer rig.
You follow every lead, until it runs out or results in an arrest, or a dead end. You NEVER know how adept, capable, intent, willing, or successful someone really is until it is all over. When it comes to the possibility of someone committing a terrorist act, in this day and age, you can't just blow it off because they LOOK like total morons. I ran across plenty of people looked for all the world like they couldn't tie their shoes or wipe their bellybutton without a set of instructions and some one there to read them. But they were pretty successful as criminals, despite the fact that they weren't Mensa candidates.