STURGIS, S.D. (AP) — A Rapid City man has pleaded not guilty to killing his girlfriend's 21-month-old son in Black Hawk last month.

Twenty-eight-year-old Thomas Pentecost was arraigned Monday. KOTA-TV reports charges against him include second-degree murder, and he could face up to life in prison if he's convicted.

Authorities say the boy suffered head trauma while Pentecost cared for him with his mother away. The toddler was declared brain dead, and he was taken off life support two days later.

Pentecost has said the boy fell and hit his head.

A message seeking comment was sent to an attorney representing Pentecost.

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