The boy directed Sgt. Harold Van Winkle to the basement when he arrived at the home Wednesday.
Detective Sgt. Robert Bracken tells The Record newspaper the girl ran out of the basement covered with blood followed by the 100-pound dog.
Van Winkle managed to get the girl to safety.
The dog charged an animal control officer and Van Winkle, who shot and killed the pit bull.
The girl was treated for bites on her arms, legs and stomach.