UPDATES: After wild chase, gunfights, day of citywide lockdown, 'it's over'; Suspects identified as Chechen brothers living several years in U.S....
By Brad Friedman on 4/19/2013, 2:01am PT  

5:50pm PT: Boston Police tweet: "CAPTURED!!! The hunt is over. The search is done. The terror is over. And justice has won. Suspect in custody." Watertown residents stream into streets to cheer police as cars roll back out of town...

5:47pm PT: Local media: Second "suspect alive, in custody, and they're asking for a medic. It's over." Applause heard breaking out around scene. || Boston Police tweet: "Suspect in custody. Officers sweeping the area."

4:31pm PT: "Barrage of gunfire" heard in Watertown. "Body found on a boat," reports NBC's Pete Williams. Area locked down, officials respond, reports of suspect surrounded...unclear whether person is still alive...

12:51pm PT: Noteworthy developments since I last checked in here. The suspects are brothers from Chechnya and have been in the U.S. for two years or more. The one who was killed is 26-year old Tamerlan Tsarnaev. The one still on the lam is 19-year old Dzhokhar. Here's another good timeline of the overnight events through 8:40am ET today as the city remains shut down during the on-going manhunt...

3:15am PT: All MBTA transit trains and buses have been shut down, as the man hunt continues. Since I suspect this is all going to be over, one way or another, by the time I wake up, and since it's the second near-all-nighter I've had here in a row, I'm going to try and hasten things by going to sleep. Though I'll likely still be following along and retweeting on The Twitters.

1:55am PT: It's been a wild night, where we've been trying to keep up with and/or make sense of developments via Twitter.

So far, one MIT officer has been shot dead. Another local law enforcement official is in critical condition after a gunfight with the alleged Boston Marathon bombing suspects. One of those suspects, the one seen in the black hat in photos released by the FBI earlier today, is now dead, according to officials.

The other suspect, in the white hat, is being pursued in the Watertown area at this time, where residents have been asked to stay inside, lock their doors, and do not open it unless it is for the police who are going yard-by-yard searching for the second suspect. He is believed to be armed and very dangerous.

Here, via CBS Boston, is what happened up until now, over the past 5 hours or so, according to a description offered by the Middlesex District Attorney...

Authorities launched an immediate investigation into the circumstances of the shooting. The investigation determined that two males were involved in this shooting.

A short time later, police received reports of an armed carjacking by two males in the area of Third Street in Cambridge. The victim was carjacked at gunpoint by two males and was kept in the car with the suspects for approximately a half hour. The victim was released at a gas station on Memorial Drive in Cambridge. He was not injured.

Police immediately began a search for the vehicle and were in pursuit of the vehicle into Watertown. At that time, explosive devices were reportedly thrown from car by the suspects. The suspects and police also exchanged gunfire in the area of Dexter and Laurel streets. During this pursuit, an MBTA Police officer was seriously injured and transported to the hospital.

During the pursuit, one suspect was critically injured and transported to the hospital where he was pronounced deceased. An extensive manhunt is ongoing in the Watertown area for the second suspect, who is believed to be armed and dangerous.

The case is being investigated by local, state and federal authorities working in cooperation. The Massachusetts State Police Bomb Squad is assessing and removing any potentially explosive devices that may have been thrown on the street in Watertown by the suspects.

NBC has more details on the firefight and the other extraordinary events throughout the night.