How does one become radicalized ? Can we reverse the process, develop a program and teach it in schools and communities ?

One of the things you notice whenever we have some of these violence and terrorist attacks is the shock family and friends express when the perpetrators are identified. You often hear friends and family say the suspects seemed normal, friendly and doesn't have any atom of violence in them. Then as more and more information begins to come to light, the language shifts to when, where and how the individual was radicalized..So i want us to discuss how the process begins...Is there any sign or signs the society, family and friends usually miss as one become radicalized...