Its curious how the media seems to home in on the fact that these two moslem brothers were so "educated" and "socially agreeable" with their peers at school etc. A couple of nice ordinary guys?
They seem to expect terrorists to be morons and maladjusted introverts.
Iniquity covers many human traits with the purpose of achieving sinful acts. Sin is not ignorant of what people want to see and hear and therefore provides sweet tastes and beautiful images. Just like Satan who is the master of all things subtle. Basically tell them what they want to hear then, in disguise, smile and commit the sin.