So the attacker (if indeed the story is true) is a convert. Probably the most dangerous group, followed by those from a Muslim background who largely ignored their mainstream religious upbringing before suddenly "reconnecting" under the malign influence of a radical preacher.
Unfortunately I don't think we'll ever stamp this out as, looking beyond this particular religion, it's basically a question of misfits suddenly finding something that explains their inadequacies and puts them at the centre of the drama. Even in Europe, we had the appeal of quasi-religions such as fascism and communism giving various inadequates a sense of power over others, and there might be other such poisons to come.
Until then, gather intelligence, intelligence and more intelligence and try to ignore the siren voices of the likes of Farage and Le Pen.