Boston Marathon bombing (59 images)

U.S. President Barack Obama makes a statement on the progress of the investigation of the tragedy in Boston in the White House Press Briefing room on April 16, 2013. Although the bombings have been called a terrorist act, investigators say it was too early to say the attacks were carried out by a foreign or domestic group. UPI/Dennis Brack/Pool

U.S. President Barack Obama makes a statement on the progress of the investigation of the tragedy in Boston in the White House Press Briefing room on April 16, 2013. Although the bombings have been called a terrorist act, investigators say it was too early to say the attacks were carried out by a foreign or domestic group. UPI/Dennis Brack/Pool

U.S. President Barack Obama makes a statement on the progress of the investigation of the tragedy in Boston in the White House Press Briefing room on April 16, 2013. Although the bombings have been called a terrorist act, investigators say it was too early to say the attacks were carried out by a foreign or domestic group. UPI/Dennis Brack/Pool

AN NYPD police officer stands guard outside of the New York Stock Exchange on Wall Street In New York City on April 16, 2013. New York City and Washington, D.C are tightening security in wake of the blasts at the Boston Marathon which killed three and injured at least 176. UPI/John Angelillo