OK, you've vented. Now answer the question. It is a serious question. What would you have them do? If you can't come up with a reasonable answer then you see the problem.
We can't arrest people for what they might do. There's nothing new in that. It is up to the authorities to keep tabs on these people, to gather intelligence, to find out what threats they represent and what they are up to. They may be doing all that right now, they aren't going to tell us. The sarcasm and ranting are out of place. You are expecting something that can't be done. You want instant answers, people rounded up, whatever, and it doesn't work that way.
Since they operate a school ( university ?) how about getting an enrollment list, current and past, and check for out of date visas. Of course, they have no foreign students attending -right? Which agency does that and how does one get a check like that started?