It sounds very militant, idealistic and revolutionary, but in fact many of these terrorist actions and activities are taking place in usual open environments, counting on the ignorance and the indifference of us, the daily serious tax-paying citizens. The Stratfor analysis made a round-up of the latest cases from the US, including regarding the dirty bombs.
The profile of Faisal Shahzad, involved in the Times Square incident, is offering an example of a failure. A failure of integration - not necessarily a political failure - the absence of offering to the immigrants a different way to insert into the society. And a failure of the security policies of various US agencies in mapping preventively security threats.