Boston’s WCVB has more astonishing raw footage from the early hours gunfight in Watertown, Mass., where police closed in on the suspected Boston Marathon bombers, who answered with (according to several reports) machine-gun fire and thrown explosives. Science journalist Seth Mnookin, who teaches at MIT, was on the scene—and tweeted it. The night’s developments began with the murder of a police officer at MIT, followed by the Watertown gunfight, and a manhunt for one of the suspects. The other suspect apparently died after the firefight.

Much of this information comes from Twitter, in particular from relayed reports from police scanners in the area. Needless to say, news of this sort is subject to revision. But the Boston Globe is among the more established sources that confirms the outlines of what happened overnight. At first it was unclear whether the MIT incident was related to the marathon bombings—but the subsequent exchange of heavy fire between police and the suspects, who seemed to have explosive devices in their possession, tended to dismiss most doubts.

Update — This post has been corrected to include new information. We now know the two suspects are apparently brothers from in or near Chechnya. The elder died in a firefight and the younger is still at large.