And how did this animal enter the U.S.?
Three people were injured (mercifully, there were no deaths), and the would-be bomber, identified as Akayed Ullah, was taken to a nearby hospital.
It is a good thing for New York City and the country that the terrorist wannabe did not understand how to build a proper pipe bomb. If he had, there likely would be many people dead and maimed, much economic damage, and another wave of fear would grip the city and the nation.
2) Who is David Cattler and why is that relevant to Flynn's plea?
Cattler's position on the NSC senior staff was created by Flynn, one of two new deputy assistant positions he created within the NSC.
3) This is important because Cattler was approved and granted TS/SCI clearance along with the other senior NSC staff hand picked by Flynn - this allows him access to see raw SIGINT without violating national security - something denied to many other Trump appointees in Jan/Feb: