STURGIS, S.D. — A South Dakota teenager has pleaded not guilty by reason of insanity to a first-degree murder charge in the shooting death of a girl from Wyoming whose body was found in his basement.

Also Thursday, 17-year-old Michael Gavin Campbell entered a not guilty plea to an alternate second-degree murder charge. He is charged as an adult. His lawyer is trying to get the case moved to juvenile court.

The boy was indicted Wednesday in the killing of 16-year-old Shayna Ritthaler of Upton, Wyoming, whose body was found Oct. 7 in the basement of the defendant’s home near Sturgis, where he lived with his mother.

Meade County Sheriff Ron Merwin has said Ritthaler was shot once in the head.

Investigators are trying to determine how the two met.