A State Police K-9 cruiser is parked near yellow police tape at Massachusetts Avenue on the MIT campus after the campus was shut down by police when a report came in of an individual wearing body armor and carrying a rifle on Massachusetts Avenue and on campus. Police found nothing and the report was later determined to be a hoax.
John Tlumacki/The Boston Globe via Getty
Boston police on bicycles patrol Commonwealth Avenue.
Michael Dwyer/AP
Cars stop at a checkpoint at the entrance of Los Angeles International Airport after security was increased. California emergency management officials activated a statewide threat assessment system after the explosions.
Kevork Djansezian/Getty
A New York Police Department officer inspects a man's bag in Grand Central Terminal in Manhattan.
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New York City police officers patrol outside the Barclays Center prior to a Brooklyn Nets basketball game.
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New York Police Department officers gather at the edge of Times Square. The city has announced it will implement heightened security measures in response to the April 15 bombings at the Boston Marathon.
New York Police Department vehicles are lined up at the edge of Times Square.
Helicopters fly near the construction site of One World Trade Center, seen from Jersey City, New Jersey. New York officials are securing the city in the wake of the Boston explosions.
Julio Cortez/AP
A police officer with his K-9 companion keeps guard as a Long Island Rail Road train from New York City arrives at the station. According to reports, at least three people were killed and more than 100 injured in two blasts at the Boston Marathon.
Bruce Bennett/Getty
A security guard ushers people away from the windows of a hotel on Huntington Avenue near the finish line after two bombs exploded during the 117th Boston Marathon.
A Boston police officer patrols the area near the finish line following the explosions at the marathon. Authorities carried off the injured while stragglers were routed away from the site of the blasts.
Josh Reynolds/AP
U.S. Secret Service and U.S. Park Police officers stand guard on Pennsylvania Avenue in front of the White House. Security around the White House was tightened after the explosions.
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President Obama talks on the phone with FBI Director Robert Mueller to receive an update on the explosions. Seated with the president are Lisa Monaco, assistant to the president for homeland security and counterterrorism, and Chief of Staff Denis McDonough.
Pete Souza/The White House
