I found this:
Tamerlan and Dzhokhar Tsarnaev only had one real gun and one pellet gun. Investigators believe because the officer's holster had a locking system, they apparently couldn't get the gun out.
Officer Sean Collier was shot in the head execution-style while sitting in his patrol car.
At 5:10 p.m. Thursday, investigators of the bombings release photographs and video of two suspects. They ask for the public's help in identifying the men.
I would think the MIT officer would be privy to such information. Photos, descriptions.
At 10:30 p.m., this MIT campus police officer, responding to a disturbance is found shot in his vehicle, apparently in a confrontation with the Boston Marathon bombing suspects.