From nojo at Stinque:
Traveling to the United States on a tourist or business visa is a straightforward process: You apply at the local embassy or consulate, sit through an interview if someone wants to know you better, pay your fees, and done. Depending on season and demand, takes three to six weeks.
This is how nineteen of the twenty 9/11 hijackers entered our country. The twentieth arrived on a student visa.
None were refugees.
Were a similar plot hatched today, it would likely follow a similar path. Of the various means to reach U.S. soil, refugee status is the most tortuous — a series of referrals, interviews, reviews and background checks that can take two years.