What does it take to infiltrate a terror group?

When it comes to battling terror groups like ISIS, few tools are as effective as human intelligence. It took years to infiltrate key al Qaeda operatives. The CIA did it with the help of a double agent named Morten Storm.

Storm was a Danish boxer, who was radicalized after he converted to Islam. He quickly rose into the upper ranks of al Qaeda. When the large number of civilian deaths convinced him to turn on the group, Storm helped take out one of its top leaders, Anwar al-Awlaki.

CNN terrorism analyst Paul Cruickshank helped tell Storm's story. He is a co-author of the new memoir "Agent Storm: My Life Inside al Qaeda and the CIA."