The following is a script from "The Boston Bombings" which aired on April 21, 2013. Scott Pelley is the correspondent.
A five-day battle in the war on terror leaves us with a lot of questions. What was the motive for the marathon attack? Where did the terrorists plan to strike next with their arsenal of bombs? And how did the manhunt stop them in only a little over 100 hours?
Tonight we have the inside story from one of the leaders of that hunt, Boston Police Commissioner Ed Davis. Last Monday afternoon, Davis was in the stands at the finish line. All was going well so he left to take a call. One of the city's favorite celebrations was coming to an end. The marathon is always on the day that marks the start of the American Revolution. But suddenly, Ed Davis and a task force of more than 4,000 would soon find themselves defending Boston on Patriot's Day.
Scott Pelley: When you arrived, what did you see?
Ed Davis: I saw a bombing incident that I'd only seen in places overseas.
Ed Davis: I saw Officer Michael Barrett from the Boston Police Department wade into an unbelievable scene of carnage and put the fire out on an individual that was still on fire and then grab belts off people and put tourniquets on the man's legs so he could save his life.
Scott Pelley: This is your city. You're enormously proud of it and these people had done this on Patriot's Day.
Ed Davis: It certainly made me resolve to find these people quickly and to hold them accountable.
Scott Pelley: You were gonna get them.
Ed Davis: Yeah, I was.
Scott Pelley: You made that promise to yourself.
Ed Davis: I did. And to several other people too.
Ed Davis' promise was to the three who were killed and more than 170 wounded. The first calls he made were to Richard DesLauriers, head of the FBI's Boston office, and Colonel Timothy Alben of the state police. The FBI took the lead and the marathon became a sprint.
Ed Davis: Very quickly we established a command post at the Westin Hotel in the ballroom. And that expanded from about a dozen people when I first walked in the door to 100 people in the first hour.
They found bomb parts right away. Evidence cascaded in.
Ed Davis: It's a logistical nightmare. We found very quickly that we needed a place to process this evidence. So a warehouse was obtained, very quickly computers were brought in from the FBI and the state police and the Boston Police and set up to review video.
Among the thousands of faces, they wanted to isolate people who didn't seem surprised.
Ed Davis: And particularly one of the FBI agents who's a technical expert did a tremendous job and really was the person that was able to get to the bottom of this very quickly.
Look at these people running in terror. But look deeper and see what the agent saw. This kid seems unconcerned. Turned out, he came with a backpack but he left without it, just like the older man who seemed to be with him.
Scott Pelley: And when you saw the faces of those two men you thought what?
Ed Davis: I thought about the death of the 8-year-old boy, the Martin child. And how someone who didn't appear to be particularly evil could do such an evil thing.
Scott Pelley: They didn't appear all that evil to you in the video?
Ed Davis: No, they looked like college kids.
Boxing photographs courtesy of Landov Media