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

1 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

2 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

3 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)

4 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)