>> anomalies like this, the man in the white hat who after the first blast doesn't even flinch. >> so it was the absence of a reaction. your normal reaction if you hear a loud noise, you automatically will shift your head toward the direction of that loud noise. he didn't do that. he was unfazed, and that was the thing that really stood out. >> a crucial lead to follow. >> we started retracing, back this up. do we see him with anyone else? and then we do. we do see him with an individual wearing a black cap. >> investigators believe they have identified their suspects, but they don't have their names. >> we are releasing photos of these two suspects. they are identified as suspect one and suspect two. >> the two brothers are now the most wanted fugitives in america. >> they knew that with their photos out there, they were going to be identified quickly. >> after months of carefully planning their attack, the tsarnaev brothers have failed to