With Boston Marathon bombing suspect Dzhokhar Tsarnaev alert, investigators are beginning to piece together the events leading up to last week's tragedy. Tsarnaev reportedly told officials Monday that he and his brother acted alone, and that his brother Tamerlan was the driving force behind the plot, which was religiously motivated. He has also said the bombs were made per instructions found on the Internet. The suspect is unable to talk due to a gunshot wound in his neck, but is communicating via writing.
Boston Attacks Bob Leonard/AP