Police officers walk near a crime scene Friday, April 19, 2013, in Watertown, Mass. A tense night of police activity that left a university officer dead on campus just days after the Boston Marathon bombings and amid a hunt for two suspects caused officers to converge on a neighborhood outside Boston, where residents heard gunfire and explosions.(AP Photo/Matt Rourke)

BOSTON - 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.

— 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, just outside Boston. Dozens of police officers and FBI agents converge on a Watertown neighbourhood. A helicopter circles overhead.

— Around 4:30 a.m., Massachusetts state and Boston police hold a short outdoor news briefing. They 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, apparently taken from store video earlier in the evening at a 7-Eleven convenience store in Cambridge. He is wearing a grey hoodie-style sweatshirt.

— 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 one 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, Mass.

— 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.

News from © The Associated Press, 2013