
People assist an injured man after the explosions. (AP Photo/The Daily Free Press, Kenshin Okubo)

Justine Franco of Montpelier, Vt., holds up a sign looking for her missing friend, April, who was running in her first Boston Marathon. (AP Photo/Winslow Townson)

A marathon runner leaves the course near Copley Square. (AP Photo/Winslow Townson)

A man in the crowd following the explosion. (AP Photo/The Daily Free Press, Kenshin Okubo)

Firefighters tend to a man at the finish line. (AP Photo/Michael Dwyer)

Medical workers aid an injured woman at the finish line. (AP Photo/Charles Krupa)

Two police officers with rifles watch from the roof of the Lenox Hotel, overlooking the finish area, following the explosions. (AP Photo/Elise Amendola)

Gov. Deval Patrick pauses as he speaks about the explosions during a news conference as Boston Police Commissioner Edward Davis, left, looks on. (AP Photo/Bizuayehu Tesfaye)

Members of the Massachusetts National Guard wait for orders on Boston Common in the evening following the explosion. (AP Photo/Michael Dwyer)

Emergency responders comfort a woman on a stretcher who was injured in one of the blasts near the finish line. (AP Photo/Jeremy Pavia)

The second blast site is investigated and guarded by police. (AP Photo/Elise Amendola)

One of the two blast sites on Boylston Street is investigated on Monday. (Elise Amendola/AP)

Medical workers aid injured people at the finish line following the explosion. (Charles Krupa/AP)

LEFT: Medical workers aid a victim. (Charles Krupa/AP). RIGHT: The scene after the two explosions. (Bruce Mendelsohn/AP)

Police clear the area at the finish line as medical workers help the injured. (Charles Krupa/AP)

Runners’ belongings piled up at the corner of Boylston and Berkeley Streets. (Steve Brown/WBUR)

The National Guard gathers on Boston Common. (Steve Brown/WBUR)

A Boston police officer patrols the area near the finish line following the explosion. (Josh Reynolds/AP)

People react to the explosion at the 2013 Boston Marathon. (The Daily Free Press, Kenshin Okubo/AP)

People react to the explosion at the 2013 Boston Marathon. (The Daily Free Press, Kenshin Okubo/AP)

Women react as they leave the area of the explosion. (Josh Reynolds/AP)

Boylston Street and Berkeley Street in the aftermath of the explosion. (Steve Brown/WBUR)

Police seal off the marathon route and move everyone out of the area. (Robin Lubbock/WBUR)

Medical workers aid an injured man at the finish line. (Charles Krupa/AP)

A Boston police officer clears Boylston Street following the explosion at the finish line. (Charles Krupa/AP)

Medical responders run an injured man whose limbs were severely injured. (Charles Krupa/AP)

Medical workers wheel the injured across the finish line. (Charles Krupa/AP)

Medical workers aid injured people at the finish line. (Charles Krupa/AP)

Medical workers aid injured people at the finish line. (Charles Krupa/AP)