police s.w.a.t. teams going door-to-door in watertown. they're asking people to stay home, lock your doors. do not answer your doors unless you see a bona fide law enforcement official outside. >> this is an ongoing investigation. we can't get into details on the descriptions of the suspects or the names. we're trying to get information out to the people who live here, that they should stay in their homes, and not open their doors unless police officers are there. there's a 20 block perimeter around the location that chief devoe just talked about. we are concerned about securing that area and making sure that this individual is taken into custody. we believe this to be a terrorist. we believe this to be a man who's come here to kill people. >> if you're just joining us, there was a shoot-out overnight. and suspect number one in the boston marathon attack killed. suspect number two on the loose. we're going to take a look at some amateur video from the