So far the screening methods available give no guarantee of preventing atrocities, and that they are more than a rather ineffective defence, quite often either previously unknown or even known and recognised risky individuals seem to penetrate them and merge invisibly into the population.
The whole system needs a major study to see what improvements can be made, and what is going to be done about the threat's that are identified, how are they to be rendered harmless to the public?
We have neither the means, moral right (Where the threat is only theoretical) or will to jail all suspects for the rest of their lives, nor can we Deport them all for a variety of reasons, as no doubt many are British Nationals.
And lets be honest, the Government has "Mislaid" the whereabouts and identity of most of them anyway, despite us being the nation that tops the list for spying on its own population.