A Stearns County jury on Friday found a 34-year-old man guilty of two counts of second-degree murder in the shaking death of his infant son.

Robert J. Kaiser, of Farming Township, was found not guilty on the more serious charge of first-degree murder. He faces up to 40 years in prison, which will be determined at sentencing scheduled for Jan. 12.

According to the criminal charges, Kaiser was angry that his 2-month-old son, William John Polries-Kaiser, was not allowing him to sleep and violently shook the boy to the point of inflicting a fatal brain injury at the family’s home in south Albany.

The father was caring for the boy on Aug. 27, 2014, while the mother was away for the day. When she returned in the afternoon, she noticed her son “seemed different,” the complaint read. The boy was taken to Albany Hospital, then transferred by air ambulance to a Twin Cities hospital.

The mother told investigators Kaiser had texted her earlier that afternoon to say their baby was keeping him awake. Seeking to explain the injury to authorities, Kaiser said he fell while holding his son and demonstrated on video how that occurred.

The boy died of traumatic brain injury, according to the Ramsey County medical examiner’s office. “The medical findings suggest that the mechanism for [the boy’s] injury was shaking,” the complaint continued.

The autopsy and further investigation revealed that the boy had broken ribs and other injuries in various stages of healing that likely also were the result of abuse.