NEW YORK — A young Brooklyn boy who vanished while walking home from a day camp in one of the safest parts of the city was killed and dismembered by a stranger he had turned to for help after getting lost, police said Wednesday. An intense search for the missing 8-year-old, Leiby Kletzky, ended with the gruesome discovery of pieces of his dismembered body inside the home of a man who had been seen with the child around the time he disappeared, police said. Police Commissioner Raymond Kelly said the 35-year-old suspect, Levi Aron, made statements implicating himself in the boy’s death.