Why can't we stop extremists? Because they are unpredictable

People are angry that 'known' extremists were able to carry out Friday's Paris attacks. But the resources needed for such sweeping surveillance are huge Officials in France and Belgium are under pressure from frightened and angry citizens, who want to know how their security services let men they knew to be involved in extremism carry out Friday's attacks in Paris. At least three of nine people now known to have been involved in the Paris strikes had been identified by security services as poten...