In this 2010 photo provided by the Massachusetts Bay Transportation Authority, Richard Donohue Jr., left, and Sean Collier pose together for a photo at their graduation from the Municipal Police ... more 
In this 2010 photo provided by the Massachusetts Bay Transportation Authority, Richard Donohue Jr., left, and Sean Collier pose together for a photo at their graduation from the Municipal Police Officers' Academy. On Thursday, April 18, 2013, Massachusetts Institute of Technology Police Officer Collier was fatally shot on the MIT campus, and transit police officer Donohue was shot and critically wounded. Authorities allege that Boston Marathon bombing suspects Tamerlan and Dzhokhar Tsarnaev were responsible. (AP Photo/Massachusetts Bay Transportation Authority) less 
1 / 30
Associated Press | Photo By Massachusetts Bay Transportation Authority
Sun, Apr 21, 2013 9:07 AM EDT