On Thursday, the FBI arrested three people in the Northeast connected to the failed Times Square bomb plot. Their main role seems to have been in financing the exploits of Faisal Shahzad through what’s known as the Hawala system. What is Hawala? How does it work? Is there a way to stop it effectively? How much money changes hands like this? We ask Dr. Rachel Ehrenfeld, author of “Funding Evil: How Terrorism is Financed and How to Stop It”.