An Alabama teenager has pleaded guilty in the death of his 9-year-old half-sister, who was hanged from a tree in their yard.

Court documents show 18-year-old John Dillon Salers pleaded guilty to murder Tuesday in St. Clair County. A judge sentenced him to 20 years in prison.

Salers was only 14 in May 2012, when half-sister Katelynn Arnold was found hanging in a tree outside the rural home they shared with relatives.

Authorities at the time said the girl was outside playing when her aunt realized she was missing. She went outside to find the child hanging from a tree by a cotton rope.

Salers was initially charged as an adult with capital murder but pleaded guilty to a reduced charge.

Court documents don't indicate a motive for the killing.