One suspect in the Boston Marathon bombing is in custody, wounded, and another is on the loose in Watertown, Mass., according to The Boston Globe. The events in Watertown started with the fatal shooting of an MIT police officer in Cambridge, a carjacking followed by a car chase into Watertown (about 4 miles away), then a huge firefight in which the suspects reportedly lobbed explosives at police. This amateur video of the firefight in Watertown was uploaded to YouTube.
Reuters is providing live updates.
UPDATE (4:30 ET): Police say the "dark hat" suspect was pronounced dead on arrival at the hospital. This is Boston Police Commissioner Edward Davis:
One suspect dead. One at large. Armed and dangerous. White hat suspect at large.
— Edward Davis (@EdDavis3) April 19, 2013
Here's context for the video above, from CBS News: