Twitter users are reporting multiple gunshots in Watertown, and local TV station WCVB is reporting that a body (or blood) has been found in a boat in a Watertown backyard. They're live-streaming right here. Reporters are being told by police to back off from the scene.
UPDATE 4:06 PM: Now the Boston Globe is reporting that the other Marathon bombing suspect is "pinned down in Watertown."
UPDATE 4:11 PM: This information, again, is coming from WCVB's livestream: FBI, SWAT, ATF, and Boston Police are pulling around the house. A neighbor estimates he heard around 21 shots.
UPDATE 4:48 PM: WCVB reporters are saying their sources say it is the suspect and that he is moving. They also say that the police are moving slowly for fear of booby-trapped explosives.
UPDATE 4:51 PM: There are loud and repeated pops on the WCVB livestream. NBC says there have been twelve pops in the last couple minutes. They might not be gunshots, as many sources are reporting.
UPDATE 4:56 PM: NBC's Pete Williams says his sources indicate that the suspect has been wounded, and that he's been in the boat for much of the day.
UPDATE 5:02 PM: The Globe is reporting that the pops were flash-bangs, which the Boston PD was using to disorient the suspect. Their sources say that they have seen the suspect sit up.
UPDATE 5:11 PM: A different police helicopter with a much brighter light has been called in.
UPDATE 5:18 PM: The NBC affiliate is saying that the suspect is "covered in blood."
UPDATE 5:37 PM: Whoa: The Globe is now tweeting that three other people have been taken into custody in the town of New Bedford as part of the bombing investigation.
UPDATE 5:44: Multiple sources are reporting that the suspect is in custody, alive. Boston PD says he's in custody, but haven't reported about whether he's alive or not:
Suspect in custody. Officers sweeping the area. Stand by for further info.
— Boston Police Dept. (@Boston_Police) April 20, 2013