tamerlan remains focused, barely missing a stride. it's here that the brothers interact. they seem relaxed. dzhokhar resting at times. tamerlan moving, moving, working out before two bombs exploded near the finish line of the boston marathon. >> fbi agents did see this tape. what they did in their rush is they took screen grabs, because this cape to their attention pretty early on in the investigation. one other note, the man who was killed in florida, the friend of tsarnaev's, inrahebragim todashe worked of out that gym years earlier. >> deborah feyerick, thanks so much. ahead on sta"starting poin, the mcdonald's diet. the ceo of the fast food chain says he lost 20 pounds and did it while still eating