Police emptied the streets of suburban Watertown on Friday in a house-by-house search for a second suspect in the Boston Marathon bombing, the day after killing his brother in a shootout.
The night of shooting and explosions in the streets followed the authorities' release Thursday of video footage of the two suspects.
Here is a timeline of events:
Thursday, about 5:10 p.m.
The FBI announces law enforcement has identified two men suspected of planting the pressure cooker bombs that killed three people and injured 176 at the Boston Marathon on Monday. Video footage released by the FBI show a man known as suspect No. 1 wearing a dark baseball cap. He was later identified as Tamerlan Tsarnaev, 26.
Suspect No. 2, later identified as Tsarnaev's brother, Dzhokhar, 19, was wearing a white cap backwards in the images. The 30-second videos are played repeatedly on national television, and photographs of the suspects are posted online.
Thursday night at 9:04 p.m.
Russian language social networking site VK shows someone logged for the last time out of what appears to be Dzhokhar Tsarnaev's page. The site had been accessed via mobile device.
Thursday night around 10:20 p.m.
Shots are fired at the Massachusetts Institute of Technology campus. At some point, two men rob a 7-Eleven store on campus.
Police discover MIT campus police officer Sean Collier, 26, shot multiple times in his car in an apparent confrontation with the suspects. He was transported to Massachusetts General Hospital and pronounced dead.
Shortly after 10:30 p.m.
Police say the two brothers carjack a Mercedes SUV. The owner of the car is held hostage for about a half hour, but is then released. Police chase the SUV into the Boston suburb of Watertown. During the chase, the suspects throw explosives from the car and exchange gunfire with police.
A transit police officer is hurt in the shootout. Witnesses report hearing dozens of gunshots.
Tamerlan Tsarnaev is hit during the shootout. He is taken into custody, transported to Beth Israel Deaconess Medical Center and later pronounced dead.
Before 1 a.m. Friday
A huge manhunt is launched for the second suspect and hundreds of police officers and FBI agents descend on Watertown.
Between 3 and 4 a.m.
Massachusetts police announce they will conduct a door-to-door search in Watertown. Citizens are warned to stay indoors.
Around 5:30 a.m.
Train service in Boston is suspended.
Massachusetts officials announce they have expanded the shelter-in-place recommendations for the entire city of Boston, effectively putting the city in lockdown as they search for Tsarnaev.
Compiled based on media reports, official statements from law enforcement and Reuters reporting.
Reporting by Sarah Lynch and Alina Selyukh in Washingtno, Tim McLaughlin, Svea Herbst Bayliss, Stephanie Simon in Boston; Editing by Alistair Bell and Doina Chiacu