The 9-year-old boy who was struck and killed by a car while crossing Columbia Road near the Washington Street intersection in Dorchester Tuesday night has been identified, Boston police said Friday. Christopher Miles of Boston was struck by a white sedan, whose driver stopped after the accident. Police responded to the call at about 10:32 p.m. Tuesday. The boy was taken to Boston Medical Center, where he was later pronounced dead. The Boston Police Department Accident Reconstruction Team is investigating the cause, and no violations have been issued, police said.