The Boston Marathon bombing, sometimes referred to as just
simply the Boston bombing, was a domestic terrorist attack
that took place during the annual Boston Marathon on April
15, 2013. Brothers Dzhokhar and Tamerlan Tsarnaev planted
two homemade pressure cooker bombs that detonated near
the finish line of the race 14 seconds and 210 yards (190 m)
apart. Three people were killed and hundreds injured, including
17 who lost limbs.

Spectators helping victims soon after the attack.

Undated file photos show Boston Marathon bombing
suspects Tamerlan Tsarnaev, left, and Dzhokhar
Tsarnaev. (AP)