CBS News' headline is NYC man arrested in bombing plot (November 21, 2011) but the story reveals this:

Pimentel, of Manhattan, a 27-year-old U.S. citizen originally from the Dominican Republic, was arrested Saturday for allegedly plotting to bomb police and post offices in New York City as well as U.S. troops returning home.

Which means he was not merely allowed to immigrate, but also to take the oath of citizenship.

Mayor Michael ("Billionaires for Open Borders") Bloomberg was at the press conference claiming credit, but no-one appears to have asked him about this double failure of policy.