9:02 A.M.

24 years ago, a Ryder truck packed with nearly 5,000 pounds of explosives was parked in front of Oklahoma City's Alfred P. Murrah Federal Building. In a matter of seconds, the blast destroyed most of the nine-story concrete and granite building, and the surrounding area looked like a war zone. Dozens of cars were incinerated, and more than 300 nearby buildings were damaged or destroyed. It killed 168 people, among them 19 children—most of whom were in the building’s daycare center. The youngest victim was 4 months old. On today's episode of America's National Parks, the Oklahoma City National Memorial, and one of the largest and most complex cases the FBI has ever undertaken.