9-year-old boy killed trying to stop rape of 12-year-old sister

Family says they left the kids for only a few minutes

An aunt told The New York Daily News 9-year-old Martin Cobb was "hit in the head with a brick and killed."

 The girl first told cops she was grabbed by a white man with "scraggly facial hair."  It was later learned the real bad guy threatened her unless she lied to authorities.

 WWBT reports cops gathered enough information to issue an arrest warrant for a black teenage boy.

 More here.