Well. From what we read around here, he was a quite "normal" guy until he, after visiting Britain, became "increasingly radical and angry". Maybe he was known there for these tendencies, but I think very few, if any, in Sweden knew of the extent of his radicalization.
Also, I very much doubt that he had training with explosives, from what I've read... I could have made a better bomb myself, from the descriptions of those.
"After visiting Britain"
Maybe he went to the shoe and underwear bomber training academy. Not a lot pf people get to utilize their full satisfaction or money back guarantee.