ELLSWORTH AIR FORCE BASE, S.D. — An airman at Ellsworth Air Force Base has pleaded guilty to fatally hitting his infant son in November 2016.

Twenty-four-year-old Airman 1st Class David MacDonald pleaded guilty to murder shortly after his court-martial began Wednesday at the air base.

The Rapid City Journal reports MacDonald admitted striking his 3-month-old son, Elliot, after he got frustrated trying to calm the infant at their on-base residence on Nov. 4, 2016. He had been watching the infant on his own while his wife was out working.

MacDonald told the judge he remembered striking the baby at least three times. The child was taken to Rapid City Regional Hospital and pronounced dead three days later.

An autopsy found the baby died of blunt trauma injury to the head.

Sentencing was scheduled Wednesday afternoon.