Transit officer still critical after shootout

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)CAMBRIDGE, Mass. (AP) — Doctors say the Boston transit police officer wounded in a shootout with the marathon bombing suspects had lost nearly all his blood and his heart had stopped from a single gunshot wound that severed three major blood vessels in his right thigh.