Three years ago on Marathon Monday, two explosions at the finish line rocked the city, leading to a citywide lockdown and a large-scale investigation. The FBI, Boston Police and SWAT teams searched for terrorist suspects, trying to understand who would cause such intentional harm, and why. Officials were shocked to discover that Tamerlan and Dzhokhar Tsarnaev were local, and had been embedded in the community for years. Dzhokhar, who attended Cambridge Rindge and Latin, was a college student at UMass Dartmouth at the time of the bombings.

In his latest book, CNN national security analyst Peter Bergen explores how radicalization occurs— how the Tsarnaevs and so many others went from the boys next door to radicalized terrorists, right here in the United States. Bergen joined Jim Braude and Margery Eagan on Boston Public Radio to discuss The United States of Jihad: Investigating America’s Homegrown Terrorists. To hear the interview, click on the audio link above.