On April 15, 2013, chaos erupted in Boston near the finish line of one of the world's oldest and most prestigious marathons. It was perhaps the worst terrorist attack on the United States since 9/11 and led to one of the most extensive and public manhunts in American history. False leads, false alarms and a wealth of evidence and information presented significant challenges to law enforcement, but they worked around the clock, seeking safety and justice for the American people. National Geographic goes inside the manhunt that gripped the world. With access to the FBI, Boston Police Department, victims, and those caught up in the manhunt, National Geographic presents an intimate yet comprehensive view of those five days of terror.