A woman is loaded into an ambulance after he was injured by one of two bombs exploded during the 117th Boston Marathon near Copley Square on April 15, 2013 in Boston, Massachusetts. (Credit: Jim Rogash/Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
People look on at the corner of Stuart and Dartmouth St., near the finish line after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Credit: Darren McCollester /Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
People rush out of the way on the corner of Stuart and Dartmouth St., near the finish line after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Credit: Darren McCollester/Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
Runner John Ounao crying when he finds friends after several explosions rocked the finish of the Boston Marathon in Boston, Massachusetts, on April 15, 2013. (Credit: JOHN MOTTERN/AFP/Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
A police officer directs people around the finish line at the corner of Boylston Street and Massachusetts Avenue after two explosives detonated during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Credit: Darren McCollester/Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
A runner sits near Kenmore Square after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Credit: Alex Trautwig/Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
Carlos Arredondo, who was at the finish line of the 117th Boston Marathon when two explosives detonated, leaves the scene on April 15, 2013 in Boston, Massachusetts. (Credit: Darren McCollester/Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
People walk near Kenmore Square after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Credit: Alex Trautwig/Getty Images)
Boston Marathon Bombings
Runners react near Kenmore Square after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Credit: Alex Trautwig/Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
Runners gather near Kenmore Square after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. Two people are confirmed dead and at least 23 injured after two explosions went off near the finish line to the marathon. (Credit: Alex Trautwig/Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
A runner reacts near Kenmore Square after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Credit: Alex Trautwig/Getty Images)
Boston Marathon explosions
Multiple People Injured After Explosions Near Finish Line at Boston Marathon (Jim Rogash
Getty/Images News)
Explosions At Boston Marathon Finish Line
A runner reacts near Kenmore Square after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Photo by Alex Trautwig/Getty Images)
2 Explosions At Boston Marathon Finish Line
A member of the bomb squad investigates a suspicious item on the road near Kenmore Square after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. Two people are confirmed dead and at least 23 injured after two explosions went off near the finish line to the marathon. (Photo by Alex Trautwig/Getty Images)
2 Explosions At Boston Marathon Finish Line
A runner embraces another woman on the marathon route near Kenmore Square after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Photo by Alex Trautwig/Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
State police guard an area near Kenmore Square after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Photo by Alex Trautwig/Getty Images)
2 Explosions At Boston Marathon Finish Line
A member of the bomb squad investigates a suspicious item on the road near Kenmore Square after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Photo by Alex Trautwig/Getty Images)
2 Explosions At Boston Marathon Finish Line
(Photo by Alex Trautwig/Getty Images)
2 Explosions At Boston Marathon Finish Line
A woman is loaded into an ambulance after he was injured by one of two bombs exploded during the 117th Boston Marathon near Copley Square on April 15, 2013 in Boston, Massachusetts. (Photo by Jim Rogash/Getty Images)
2 Explosions At Boston Marathon Finish Line
A member of the bomb squad investigates a suspicious item on the road near Kenmore Square after two bombs exploded during the 117th Boston Marathon on April 15, 2013 in Boston, Massachusetts. (Photo by Alex Trautwig/Getty Images)
2 Explosions At Boston Marathon Finish Line
A man is loaded into an ambulance after he was injured by one of two bombs exploded during the 117th Boston Marathon near Copley Square on April 15, 2013 in Boston, Massachusetts. Two people are confirmed dead and at least 23 injured after two explosions went off near the finish line to the marathon. (Photo by Jim Rogash/Getty Images)
2 Explosions At Boston Marathon Finish Line
A man is loaded into an ambulance after he was injured by one of two bombs exploded during the 117th Boston Marathon near Copley Square on April 15, 2013 in Boston, Massachusetts. Two people are confirmed dead and at least 23 injured after two explosions went off near the finish line to the marathon. (Photo by Jim Rogash/Getty Images)
2 Explosions At Boston Marathon Finish Line
A man is loaded into an ambulance after he was injured by one of two bombs exploded during the 117th Boston Marathon near Copley Square on April 15, 2013 in Boston, Massachusetts. Two people are confirmed dead and at least 23 injured after two explosions went off near the finish line to the marathon. (Photo by Jim Rogash/Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
BOSTON, MA - APRIL 15: Two blood stained feet of a man hangs outside an ambulance outside a medical tent located near the finish of the 117th Boston Marathon after two bombs exploded on the marathon route on April 15, 2013 in Boston, Massachusetts. (Credit: Jim Rogash/Getty Images)
Boston Marathon Bombing
A video grab shows the victims of one of the blasts at the finish line of the Marathon in Boston, Massachusetts on April, 15, 2013. At least two people were killed and 23 others wounded when two explosions struck near the finish line of the Boston Marathon, sparking scenes of panic, police said. (Credit: Marc Hagopian/AFP/Getty Images)
2 Explosions At Boston Marathon Finish Line
A man is loaded into an ambulance after he was injured by one of two bombs exploded during the 117th Boston Marathon near Copley Square on April 15, 2013 in Boston, Massachusetts. Two people are confirmed dead and at least 23 injured after two explosions went off near the finish line to the marathon. (Photo by Jim Rogash/Getty Images)
Multiple People Injured After Explosions Near Finish Line at Boston Marathon
The bandaged leg of a man hangs outside an ambulance outside a medical tent located ear the finish of the 117th Boston Marathon after two bombs exploded on the marathon route on April 15, 2013 in Boston, Massachusetts. (Credit: Jim Rogash/Getty Images)
2 Explosions At Boston Marathon
Bystanders pushed back to Stuart Street (Photo from WBZ's Jim Armstrong)
2 Explosions At Boston Marathon Finish Line
(Photo from WBZ's Jim Armstrong)
2 Explosions At Boston Marathon Finish Line
Empty streets near the site of the explosion. (Photo from WBZ's Jim Armstrong )
2 Explosions At Boston Marathon Finish Line
WBZ's Jim Armstrong reports that the crowd looking on remained mostly silent.
2 Explosions At Boston Marathon Finish Line
This photo, from WBZ's Jim Armstrong, shows empty streets near Boston's Copely Square.
2 Explosions At Boston Marathon Finish Line
Photo from WBZ's Jim Armstrong
2 Explosions At Boston Marathon Finish Line
(Photo from WBZ's Jim Armstrong)
From WBZ's Jim Armstrong
CBS Boston's Jim Armstrong
2 Explosions At Boston Marathon Finish Line
Two explosions shattered the Boston Marathon finish line on Monday, April 15, 2013. (credit: CBS News)
2 Explosions At Boston Marathon Finish Line
Two explosions shattered the Boston Marathon finish line on Monday, April 15, 2013. (credit: CBS News)
2 Explosions At Boston Marathon Finish Line
Ambulances are seen near the finish line of the Boston Marathon where there were two explosions on Monday, April 15, 2013. (credit: CBS News)