James Sanders had been charged with second-degree murder in the death of Elaine Sepulveda. He agreed to plead guilty to the lesser charge and was sentenced in Coupeville to 8 1/2 years in prison.
He apologized in Island County Superior Court to Sepulveda's family. Relatives on both sides were in tears.
Sepulveda disappeared from her Oak Harbor home in November, and there was a two-month search until her body was found Jan. 14 buried in a compost pile at the home of Sanders' grandfather.
Court documents say the grandfather told police that Sanders said he had killed the girl accidentally while trying to prevent her from committing suicide.