A 15-year-old Redlands boy who strangled his sister's 8-year-old playmate and then tossed the body into a trash dumpster was convicted of first-degree murder. Raymond William Gray Jr., who remains in custody at San Bernardino County Juvenile Hall without bail, is expected to be sentenced next month to a maximum of 10 years with the California Youth Authority. The teen-ager lured the girl, Bonnie Norcross, into his bedroom last November and strangled her. He threw her body into a cardboard box, filled it with garbage and tossed the box into a trash dumpster. Gray then went to a friend's house to watch Monday night football.