A 32-year-old man, bothered that his infant son was not allowing him to sleep, shook the 2-month-old to the point of inflicting a fatal brain injury, according to charges filed in Stearns County.

Robert J. Kaiser, of Farming Township, was charged with second-degree unintentional murder in the boy's death on Wednesday, one week after Kaiser violently shook the child at the family's home south of Albany.

Kaiser, charged Friday, remains jailed in lieu of $500,000 bail.

According to the criminal complaint:

Kaiser was caring for the boy on Aug. 27 while the mother was away for the day. When she returned in the afternoon, she noted that her son "seemed different," the complaint read. The boy was taken to Albany Hospital and 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.

Explaining the injury to authorities, Kaiser said he fell while holding his son and demonstrated on video how that occurred.

Dr. Mark Hudson, a child abuse expert, watched the video and advised that the boy's injury was inconsistent with Kaiser's version of events.

The boy died from 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 healing of broken ribs and other injuries that likely were the result of abuse.