Both Tamerlan and Dzhokhar Tsarnaev and Ibragim Todashev were regulars at Wai Kru, a martial arts gym in Boston's Allston neighborhood. It was this gym where the Tsarnaev brothers were seen just three days before the Boston Marathon bombing. They arrived with a third, as-yet unidentified individual, seen in the photo at right.

Gym owner John Allan told Greater Boston's Emily Rooney what happened when the brothers showed up at the gym three days before the bombing, and how he came to hear that Tamerlan Tsarnaev might have murdered his own best friend.

Watch the full interview: