I'm sure the police are dubious about the claims of families and communities which say, "we had no idea, he gave no hint of becoming extreme".
If you discover something amazing, world-changing, and believe something so fervently that you're willing to kill and die for it, you tend to mention it to families and friends and try and persuade them to see the light too.
The police aren't naive, they know that they are being lied to....
I've just read this thread and have decided not to read it again, The Watcher are you even thinking about what you are saying? Imagine how you would feel reading that if you were a Muslim.