If you think about it, maybe these terrorists just had a bad upbringing. (for example maybe their parents informed them of their radical/terrorist views and their children sought to carry it out.) Many serial killers today are serial killers because they were raised wrong.
I don't think any of these "terrorists" used ideas of their own and/or had some sort of religious "epiphany".
I hope no one views my statement as if I am defending them. I'm not. I hate terrorists myself.