The hunt for the two brothers suspected in the Boston Marathon bombings evolved rapidly Thursday and Friday, ending with one suspect dead and the other captured alive.
Authorities ordered a lockdown of Boston and several surrounding communities Friday after engaging in an overnight battle with the suspects, who police say were armed with guns and explosives. The young men allegedly robbed a convenience store before shooting a campus police officer to death at the Massachusetts Institute of Technology, authorities said.
The pair then reportedly fled in a hijacked SUV, only to get into a firefight with police in the suburb of Watertown. The gun battle left one of the brothers dead. The other escaped and was captured Friday night.
Here's how the violent events transpired, according to authorities and law enforcement sources:
April 18, 5 p.m. (all times ET and approximate) The FBI releases photos and a surveillance video that show two men, one wearing a white baseball cap and the other wearing a black cap. Each carries a backpack in the footage. The FBI says they should be considered "armed and extremely dangerous."
7:10 p.m. NBC News' Pete Williams reports that the FBI has begun receiving names in response to its release of photos.
10:20 p.m. Gunshots are reported on the MIT campus. It is unknown at this time whether or not injuries have occurred. The site is considered "active and extremely dangerous," according to a university alert, and responders cordon off the area.
Around 10:30 p.m. An MIT police officer is found shot in his vehicle. He is taken to Massachusetts General Hospital and pronounced dead. One of the suspects is later seen on a surveillance tape robbing a convenience store in Cambridge, officials tell NBC News. The robbery is believed to have occurred before the MIT officer was killed. Shortly after the shooting, police receive a report of an armed carjacking in a separate section of Cambridge. The carjacking victim was held at gunpoint by two men for half an hour before being released, unharmed, at a gas station on Memorial Drive in Cambridge, according to a statement by the Middlesex District Attorney.
Some time after—it's unclear exactly when—police pursue the carjacked vehicle into Watertown. Explosive devices are reportedly thrown from the SUV, according to the district attorney's statement. A Boston transit police officer is seriously injured. One of the suspects is critically injured and later pronounced dead, according to the statement.