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Investigation, and its hard to say exactly how he received that injury. there was certainly a shoot-out in watertown. there were explosives thrown. so thats being looked into right now. its hard to say exactly how it occurred. >> reporter: were learning more about the tense moments right before tsarnaevs arrest. this aerial video shows infrared images of him hiding out on a boat in the backyard of a home in watertown. according to a law enforcement source close to the investigation, after 25 min...