Mike Doucette, 27, a chimney sweep, had witnessed one of the most unsettling moments of the whole week — when one of the suspects was escaping the scene of a shootout and drove over the other, his older brother, who had been mortally wounded. The brothers were identified as Dzhokhar Tsarnaev, 19, who is now hospitalized, and Tamerlan Tsarnaev, 26, who died after the shootout.

Mr. Doucette said that the older brother was already lying in the street after the shootout and the younger one was speeding away from the scene when the undercarriage of the car caught the older brother. He said the car dragged the older brother about 30 feet, right in front of Mr. Doucette’s house, where a dark streak remains in the street. When the younger brother bumped into a police cruiser, the body was dislodged, Mr. Doucette said.