SPOKANE, Wash. -

A 23-year-old man accused in the death of his girlfriend's 18-month-old boy pleaded not guilty Monday in Spokane.

Joshua D. Burnett is charged with second-degree murder in the March 31 death of Rylee Castner.

The Spokesman-Review reports Burnett told police the boy was fatally injured in an accidental fall.

Doctors say the toddler died of head trauma that could not have come from a fall.