2:50 p.m.: With 4:09:43 showing on the race clock, an explosion goes off just short of the finish line of the 2013 Boston Marathon. Ten seconds or so later, a second explosion goes off 1500 yards away on the same street, Boylston Street, along the finish of the race.
2:57 p.m. The Boston Globe's Twitter feed reports a witness hearing "two loud booms" near the finish line.
3:14 p.m. Video emerges online of the scene following the explosions.
3:15 p.m. Runners still on the marathon course are stopped. They are rerouted to Boston Common.
3:55 p.m. Boston police detonate a suspicious object near Copley Square in a controlled explosion, per the Boston Police scanner.
4:02 p.m.: Boston police confirm 2 dead and 12 injured in the explosions via Twitter.
4:12 p.m. Boston police respond to a third explosion, at the JFK Library in Dorchester. No injuries are reported.
4:24 p.m. The AP, quoting an anonymous U.S. intelligence official, reports two undetonated explosive devices were recovered from the scene.
4:44 p.m. White House statement announces a Presidential address at 6:10 p.m. regarding the explosions.
4:44 p.m. News leaks that the Boston Bruins opted to postpone Monday's scheduled home game with the Ottawa Senators.
4:50 p.m. Boston police confirm the two explosions at 2:50 p.m. in a televised press conference with Massachusetts Governor Deval Patrick. Boston police also confirm a fire and possible explosion at the JFK Library, which they consider related. They emphasize that a link between the two marathon explosions and the third is only suspected, and not confirmed.
5:01 p.m WBZ reports cellphone service in downtown Boston has been shut off to prevent any detonation of other possible explosive devices which may be in the area.
5:06 p.m. JFK Library spokesman says the third incident may have just been a mechanical room fire, and says there were no injuries in the incident.
6:12 p.m. President Obama addresses the nation. "The American people will say a prayer for Boston tonight."
Update: A new, complete timeline of Monday's events is now available. Click here to view the updated timeline.
Additional updates as they become available will be included in SB Nation's StoryStream.