April 15, 2013. Two explosions rock the Boston Marathon, killing three people and injuring over 260. The blasts are immediately identified as a terrorist act, but many questions remain. Who planted the bombs? Why did they do it? And most pressing of all: how did they pull off an attack at one of America's most celebrated events undetected? Through in-depth analysis and expert testimony, we list the missed opportunities, security failures, and other errors that allowed the devastating events to unfold before, during, and after the bombing.
