6:55 a.m. ET: Associated Press now reports that the surviving Boston bomb suspect — Suspect Number Two — has been identified as Dzhokhar A. Tsarnaev, 19, of Cambridge, Mass. Suspect Number One (now deceased) was reportedly his older brother. Both brothers were reportedly from Chechnya, the Russian territory that has been the scene of violent terrorism and civil war in recent years.

6:28 a.m. ET: Headlines elsewhere at this hour:

One suspect in custody, another remains on the loose
- Boston Globe

Explosives Detonated in Massachusetts Standoff
- New York Times

Watertown Police Chase: Gunfire,
Explosions Reported On Scanner
- Huffington Post

One Boston Marathon suspect dead, another still on run, officials say
- NBC News

EXPECT FURTHER UPDATES …

5:35 a.m. ET: A suspect is still at large, and another is confirmed dead. Cambridge, Mass. Police statement:

Police are investigating a fatal shooting of MIT campus police officer by two men who then committed an armed carjacking in Cambridge, Middlesex Acting District Attorney Michael Pelgro, Cambridge Police Commissioner Robert Haas, and MIT Police Chief John DiFava announced this evening.
At approximately 10:20 p.m. April 18, police received reports of shots fired on the MIT campus. At 10:30 p.m., an MIT campus police officer was found shot in his vehicle in the area of Vassar and Main streets. According to authorities, the officer was found evidencing multiple gunshot wounds. He was transported to Massachusetts General Hospital and pronounced deceased.
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.

4:46 a.m. ET: It has been reported that Suspect Number One was pronounced dead at a hospital. Police are reportedly still searching for Suspect Number Two.

It was Suspect Number Two who was photographed placing a bomb next to 8-year-old Martin Richard.

3:23 a.m. ET: Photo of a suspect being detained, naked, presumably because the police were afraid he had explosives on his person. Could this be Suspect 1 from the Boston Marathon Tragedy?

3:05 a.m. ET: The Boston Globe is currently reporting that one of the suspects in Monday’s bombing is now in custody:

One suspect in Monday’s Boston Marathon bombings has been captured, according to an official with knowledge of the investigation. Another remains on the loose in Watertown after a firefight with police. Authorities have established a 20-block perimeter as they search for him.
A scene of chaos descended on Cambridge and Watertown late Thursday night and early Friday morning, as police confirmed an MIT police officer was shot and killed, and an apparent carjacking led police on a wild chase into Watertown.
Witnesses in Watertown said they heard explosions. Police officers were screaming about improvised explosive devices.
Authorities would not comment on whether the events were connected to Monday’s Boston Marathon bombings. At least one of the suspects in Watertown appeared to be a man in his 20s.
FBI agents were on the scene in Watertown.
“We are aware of the situation, we are being involved, and we are monitoring,” said an FBI representative who requested anonymity because of not being authorized to speak publicly. The FBI source said early Friday it is “too early to speculate” on a relation to the Marathon bombing.

Meanwhile, Fox News is reporting that the FBI is denying that the suspect apprehended earlier is connected to the bombing.

* PREVIOUSLY (1:55 a.m. ET) *

CNN’s Jake Tapper is reporting one man is in custody after a shooting at MIT at roughly 10:30 pm, in which a police office was killed. MIT is located in Cambridge, MA about a mile across the Charles River from the site of Monday’s bombing at the Boston Marathon. One suspect is still at large and is being sought in Watertown, MA about four miles from the bombing site.

After the shooting, there was also a car jacking at MIT, which may or may not be connected to the shooting.

Witnesses have described hearing gun shots, and loud explosions and news reports have claimed that police were calling for everyone, including media, to turn off their cell phones, in case of unexploded devices.

From listening to police scanners, police are sweeping the are for unexploded devices.

Multiple police agencies are on the scene in Watertown, including the FBI, which increases the likelihood that something significant is going on, and perhaps the man in custody and the man still at large might be connected to Monday’s bombings.

UPDATE 2:00 am -

The chaos at MIT is over, and the investigation has moved to Watertown. MIT students have been cleared to leave their buildings, and a similar alert has gone out to students at Harvard.

UPDATE 2:12 am -

Photo from the shooting at MIT via The Atlantic Wire

UPDATE 2:52 am -

CNN is reporting the man that was taken in to custody earlier, was taken only after he was completely stripped naked, because of fears he was carrying explosives. He was later taken out of the police car, still naked, and questioned up against a wall and photographed by federal officers.

Also, a SECOND man has been taken into custody. A man with a “middle-eastern” complexion, with “short cropped black hair” in handcuffs was just walked past Gabe Ramirez, a photojournalist who works for CNN.