In the hours after the blasts, investigators pore over evidence. One photo and a few seconds of footage lead to a breakthrough – and an agonizing choice.

The brothers' images are released to the public, setting off a violent chain of events. Meanwhile, clues from their past tell a complicated story.

Dzhokhar Tsarnaev is cornered into an intense standoff. As officials navigate remaining questions and suspicions, the city emerges – Boston Strong.