BOSTON (AP) — Key moments related to the search for the Boston Marathon bombing suspects, based on reports from the Middlesex County district attorney, Massachusetts State Police and Boston police.
SHOWN HERE: This undated photo provided by the Middlesex District Attorney's Office shows Massachusetts Institute of Technology Police Officer Sean Collier, 26, of Somerville, Mass., who was shot to death Thursday, April 18, 2013 on the school campus in Cambridge, Mass. Authorities said surveillance tape recorded late Thursday showed one of the Boston Marathon bombing suspects during a robbery of a nearby convenience store before Collier was shot to death while responding to a report of a disturbance. (AP Photo/Middlesex District Attorney's Office)
— At 5:10 p.m. Thursday, investigators of the bombings release photographs and video of two suspects. They ask for the public's help in identifying the men.
— Around 10:20 p.m., shots are fired on the campus of the Massachusetts Institute of Technology in Cambridge, just outside Boston.
— At 10:30 p.m., an MIT campus police officer who was responding to a disturbance is found shot multiple times in his vehicle, apparently in a confrontation with the Boston Marathon bombing suspects. He is later pronounced dead.
— Shortly afterward, two armed men reportedly carjack a Mercedes SUV in Cambridge. A man who was in the vehicle is held for about a half hour and then released unharmed at a gas station on Memorial Drive in Cambridge.
— Police soon pursue the carjacked vehicle in Watertown, just west of Cambridge.
— Some kind of explosive devices are thrown from the vehicle in an apparent attempt to stop police. The carjackers and police exchange gunfire. A transit police officer is seriously injured. One suspect, later identified as Suspect No. 1 in the marathon bombings, is critically injured and later pronounced dead.
— Authorities launch a manhunt for the other suspect.
— Around 1 a.m. Friday, gunshots and explosions are heard in Watertown. Dozens of police officers and FBI agents converge on a Watertown neighborhood. A helicopter circles overhead.
— Around 4:30 a.m., Massachusetts state and Boston police tell people living in that section of eastern Watertown to stay in their homes. They identify the carjackers as the same men suspected in the marathon bombings. Overnight, police also release a photograph of a man believed to be Suspect No. 2 wearing a gray hoodie-style sweatshirt. The image apparently was taken from surveillance video at a 7-Eleven convenience store in Cambridge. Authorities initially say the suspects robbed the store but later say they're unsure.
— Around 5:50 a.m. authorities urge residents in Watertown, Newton, Waltham, Belmont, Cambridge, Arlington and the Allston-Brighton neighborhoods of Boston to stay indoors. All mass transit is shut down.
— Around 6:35 a.m., The Associated Press reports that the bomb suspects are from a Russian region near Chechnya and lived in the United States for at least a year.
— Around 6:45 a.m., The Associated Press identifies the surviving Boston bomb suspect as Dzhokhar A. Tsarnaev, 19, who has been living in Cambridge.
— Around 8 a.m., Boston's police commissioner says all of Boston must stay in their homes as the search for the surviving suspect in the bombings continues.
— Around 8:40 a.m., a U.S. law enforcement official and the uncle of the suspects confirm that the name of the slain suspect is Tamerlan Tsarnaev, Dzhokhar Tsarnaev's older brother.
— Around 10:20 a.m., Connecticut State Police say a gray Honda CRV believed to be linked to Dzhokhar Tsarnaev has been recovered in Boston.
— Around 10:35 a.m., the University of Massachusetts Dartmouth says it closed its campus and ordered an evacuation after confirming that Dzhokhar Tsarnaev is registered there. The school says it closed the campus "out of an abundance of caution" as the search continued.
— Around 11:30 a.m., Massachusetts State Police explain that the brothers suspected in the bombings were in the Honda CRV when they carjacked the Mercedes SUV. For a while, each drove one of the two vehicles, but then ditched the Honda and reunited in the Mercedes.
— Around 12:35 p.m., state police in Watertown say officers are searching door-to-door but still have not found the bombing suspect.
Copyright 2013 The Associated Press.