Right now there is no word on if they are related to the marathon bombing.
Explosives Detonated in Massachusetts Standoff - NYTimes.com
Two young men, armed with guns and explosives in what appeared to be backpacks, engaged in a violent standoff with dozens of police on a street in Watertown, Mass., Thursday night, police and residents said.
At around 1 a.m., two residents said they heard what sounded like firecrackers began going off in Laurel St. When they looked out of their windows, they saw two young men taking cover behind a black Mercedes sports utility vehicle, in a shootout with dozens of police about 70 yards away. It marked the second violent episode late Thursday night and into early Friday morning. The chaos that descended on the residential streets came as the community was still reeling from Monday’s bombings at the Boston Marathon that killed three and wounded more than 170.
Andrew Kitzenburg, 29, said he looked out of this third floor window to see two young men of slight build in jackets engaged in “constant gunfire” with police officers. A police SUV “drove towards the shooters,” he said, and was shot at until it was severely damaged. It rolled out of control, Mr. Kitzenberg said, and crashed into two cars in his driveway.
The two shooters, he said, had a large and unwieldy bomb. “They lit it, still in the middle of the gunfire, and threw it. But it went 20 yards at most.” It exploded, he said, and one of the two men ran towards the gathered police officers. He was tackled, but it was not clear if he was shot, Mr. Kitzenberg said.