The prosecution and defense agree - Dzhokhar Tsarnaev was involved in the bombing at the Boston Marathon, the killing of MIT police officer Sean Collier, and the shootout with police in Watertown. So on Day 11, the prosecution posed this question to its expert witness: what turns a seemingly average teenager from Cambridge into a violent radical, intent on and capable of deadly acts of terrorism? Boeri and Cullen discuss the evidence presented.