ພາບຈາກການແຂ່ງແລ່ນ ມາຣາທອນ ທີ່ບອສຕັນ

A Boston police officer from the K-9 unit patrols Boylston Street near the finish line before the start of the 2014 Boston Marathon. Mandatory Credit: Greg M. Cooper-USA TODAY Sports - RTR3M2SF

Apr 21, 2014; Boston, MA, USA; Boston police officers part of the K-9 unit patrol Boylston Street near the finish line before the start of the 2014 Boston Marathon. Mandatory Credit: Greg M. Cooper-USA TODAY Sports - RTR3M2SC

Till T. Teuber of Hamburg, Germany, prepares himself before the 118th Boston Marathon Monday, April 21, 2014 in Boston. (AP Photo/Matt Rourke)

Workers move security gates into position in front of Wellesley College in the early morning before the start of the 118th Boston Marathon Monday, April 21, 2014 in Wellesley, Mass. (AP Photo/Mary Schwalm)

A State Police Special Response team patrols past posters of encouragement at Wellesley College before the start of the 118th Boston Marathon Monday, April 21, 2014 in Wellesley, Mass. (AP Photo/Mary Schwalm)

Runners in the first wave of 9,000 cross the start line of the 118th Boston Marathon Monday, April 21, 2014 in Hopkinton, Mass. (AP Photo/Stephan Savoia)

The second wave of runners make their way down Main Street during the 118th running of the Boston Marathon in Hopkinton, Massachusetts, April 21, 2014.

Elite men runners leave the start line in the 118th running of the Boston Marathon Monday, April 21, 2014 in Hopkinton, Mass. (AP Photo/Stephan Savoia)

Apr 21, 2014; Boston, MA, USA; Andrew Lembcke (left) , Brandon Petrich (middle) and Bill Januszewski hang a Boston Strong banner before the start of the 2014 Boston Marathon. Mandatory Credit: Greg M. Cooper-USA TODAY Sports - RTR3M2V4