The British spy agency MI5 has a behavioral science unit which was apparently asked to draw up a profile of a violent extremist. While noting that these days the extremists resorting to violence do so 'in defence of Islam' they went on to conclude that they couldn't offer any specific pointers that would be useful in profiling who is more or less likely to become a terrorist. The Guardian has obtained the internal MI5 document.
Its findings show that an extremist can come from among British nationals, both born and naturalized, or from among asylum seekers, or illegal immigrants. An extremist can come from a non-practicing milieu, or can be a religious novice or he can be a zealous convert. They can be Pakistani, Caucasian, or Middle Eastern; male or female; younger or older; single or married with children. In other words terrorists "are a diverse collection of individuals, fitting no single demographic profile, nor do they all follow a typical pathway to violent extremism."
In essence, then, the MI5 doesn't know what external markers identify a person who has become obsessed with killing in the name of Islam, just that there are these days some people who kill in the name of Islam.