9 a.m., April 15 -- Mobility-impaired runners kick off the 117th Boston Marathon.
10 a.m. -- The first large wave of runners, about 9,000 participants, take off from the starting line.
10:20 a.m. -- The second large wave of runners, another group consisting of approximately 9,000 participants, begins the race.
10:40 a.m. -- The final large wave of runners at the Boston Marathon starts, another group consisting of approximately 9,000 runners.
11:58 a.m. -- Rita Jeptoo of Kenya wins the Boston Marathon women's race for the second time. Her final time is 2:26:25.
12:10 p.m. -- Lelisa Desisa of Ethiopia wins the men's race of the Boston Marathon for the first time. His final time is 2:10:22.
2:18 p.m. -- The first wave of runners begins crossing the Boston Marathon finish line. The second wave begins coming in at 2:38 p.m.
2:45 p.m. -- Tagg Romney snaps a photo of his family smilng at the finish line minutes before the explosion.
2:50 p.m. -- Two blasts go off seconds apart on the north side of Boylston Street near the finish line. The blasts occur about 50 to 100 yards from each other, knocking some runners to the ground.
3 p.m. -- A fire breaks at the John F. Kennedy Presidential Library in Boston, but authorities later say it's not related to the bombings.
3 p.m. -- The Boston Globe reports that "dozens" of people are injured at the scene.
3:17 p.m. -- The FAA imposes temporary flight restrictions over Boston until further notice.
4 p.m. -- U.S. Secret Service agents expand the security perimeter around the White House complex in Washington, D.C., and shut down parts of Pennsylvania Avenue.
4:02 p.m. -- The Boston Police Department confirms that two people are dead and at least 23 injured in the explosions.
5:07 p.m. -- Citing hospitals, The Boston Globe reports that more than 100 people have been injured.
5:27 p.m. -- NBC News reports that there is no information to indicate any additional threats, citing U.S. officials.
5:48 p.m. -- Citing federal officials, CNN begins calling the explosions a "terrorist attack," although the motive of the attack remains unclear and no suspects have been arrested.
6:10 p.m. -- President Barack Obama speaks about the bombings, pledging to "bring justice" to the victims. "We'll find out who did this; we'll find out why they did this."
6:30 p.m. -- Multiple media outlets report that an 8-year-old boy is among the dead. He is later identified as Martin Richard, who was there to watch his dad race.
8:49 p.m. -- The FBI takes the lead in the bombings investigation.
8:54 p.m. -- The Boston Police Department confirms that at least three are dead as a result of the bombings.
10 p.m. -- Local media report that authorities are searching an apartment in the Boston suburb of Revere, Mass. State Police later confirmed that a search warrant was executed there.
10:42 p.m. -- Citing hospitals, The Associated Press reports that 144 people are injured, at least 17 critically.
9 a.m., April 16 -- A heavy police presence remains in Boston as the city remains on heightened alert.
10 a.m. -- Boston officials update victims numbers to three dead, 176 injured, 17 critical.
11:30 a.m. -- President Barack Obama gives a second statement, calling the bombings an "act of terror."
5:10 p.m., April 18 -- The FBI releases photos and videos of two suspects investigators believe are behind the bombing.
10:30 p.m. -- An MIT campus police officer was found shot in his vehicle in the area of Vassar and Main Streets after a convenience store robbery. He was transported to Massachusetts General Hospital and pronounced dead.
Early morning hours, April 19 -- The two suspects allegedly hijacked a car at gunpoint in Cambridge, Massachusetts, taking the driver as a hostage, then releasing the hostage. Officers began to chase, the suspects threw explosives and fired shots at the officers. Officers fired back, striking and killing a man, who was later identified as one of the bombers, Tamerlan Tsarnaev, 26. Another policeman, transit officer Richard H. Donohue Jr., was also shot, but survived.
Early hours -- Dozens of police and FBI rush into the Watertown, Massachusetts, area. Police order residents in Watertown to turn off their cell phones and they complete door-to-door searches for the living suspect. Schools and public transportation are shut down and Boston Police Commissioner Ed Davis ordered everyone in the Boston Metro area to stay indoors as the manhunt for the second suspect continued.
8 a.m. -- Sources identify the dead suspect as Tamerlan Tsarnaev, 26, and the suspect on the run as his brother Dzhokhar Tsarnaev, 19, seen here.
8 a.m.: Boston-area residents are asked by authorities to stay inside as the hunt continues for Dzhokhar Tsarnaev.
9 a.m.: The slain suspect, Tamerlan Tsarnaev, was wearing explosives and an explosive trigger when his body was recovered, a source briefed on the investigation tells CNN.
11:30 a.m.: The uncle of the Tsarnaev brothers tells reporters that he is "ashamed" to be related to the suspects. He calls those responsible for the bombings "losers." Speaking outside his Maryland home, Ruslan Tsarni says his nephew Dzhokhar Tsarnaev "has put a shame on our family, a shame on the entire ethnicity" and should turn himself in.
6 p.m.: The lockdown for the Boston area is lifted, meaning people can again leave their homes, even though a suspect remains at large. The area's public transit system, known as the T, also returns to service after being shut down most of the day.
8:15 p.m.: A person believed to be Dzhokar Tsarnaev is cornered on a boat in a yard in Watertown, law enforcement officials say.
8:46 p.m.: The Boston Police Department tweets: "Suspect in custody. Officers sweeping the area. Stand by for further info."
8:46 p.m. Police in Watertown break out in cheers, shouting "Yay!" A crowd of neighbors also cheers.
9 p.m.: A law enforcement vehicle drives by the crowd and someone asks if they have the suspect. Another police officer says, "Yes," and the crowd of residents erupts in cheers again.
10:15 a.m. May 1: Three additional suspects are taken into custody. Two of them are students from New Bedford, Mass. They are arrested on charges of making false statements to investigators and conspiracy to obstruct justice. A third student also arrested is a U.S. citizen.
3:30 p.m. July 10: In his first court appearance since the April 15 bombings, Dzhokhar Tsarnaev pleaded not guilty to 30 federal counts related to attacks.