New surveillance footage of a Boston bomber laying an explosive then fleeing the scene has been shown in court.
Footage shows Dzhokhar Tsarnaev walking through the city before pausing near the finish line, where he dropped an explosive charge that killed an eight-year-old boy.
He is seen standing in the crowd for several minutes, before calling his brother, Tamerlan. Shortly after the call, the first bomb explodes – at which point he pushes his way through the stunned crowd.
Tsarnaev managed to clear the blast zone in the 12 seconds between the first bomb exploding and his going off – but is still in the shot from a surveillance camera at the scene.