Watertown resident Christine Yajko said she was awakened at about 1:30 a.m. by a loud noise, began to walk to her kitchen and heard gunfire.
"I heard the explosion, so I stepped back from that area, then I went back out and heard a second one," she said. "It was very loud. It shook the house a little."
She said a police officer later knocked on her door and told her there was an undetonated improvised explosive device in the street and warned her to stay away from the windows.
"It was on the street, right near our kitchen window," she said.
Yajko said she never saw the suspect who was on the loose and didn't realize the violence was related to the marathon bombings until she turned on the TV and began watching what was happening outside her side door.
State police spokesman David Procopio said, "The incident in Watertown did involve what we believe to be explosive devices possibly, potentially, being used against the police officers."
Boston cab driver Imran Saif said he was standing on a street corner at a police barricade across from a diner when he heard an explosion.
"I heard a loud boom and then a rapid succession of pop, pop, pop," he said. "It sounded like automatic weapons. And then I heard the second explosion."
He said he could smell something burning and advanced to check it out but area residents at their windows yelled at him, "Hey, it's gunfire! Don't go that way!"
Doctors at a Boston hospital where a suspect in the marathon bombings was taken and later died are saying they treated a man with a possible blast injury and multiple gunshot wounds.