Jeffrey A. Davis initially told St. Paul police that his 6-week-old son had been hurt when the two bumped foreheads as Davis lifted the baby over his head, then brought him back down to kiss his forehead, according to charges filed in Ramsey County District Court.

It wasn't until after police told Davis that doctors believed the boy has "very severe permanent traumatic brain injury" that he admitted he'd become frustrated with the baby's crying and shook him until his head was "like a bobble head doll, bobbing to the front, rear and both sides," the charges said.

Davis, 32, of St. Paul, was charged last week with felony malicious punishment of a child.

The baby's injuries apparently happened March 15 when, Davis told police, he was alone with the baby all day.

"Davis stated he did not think he was shaking [the baby] hard enough to hurt him," the complaint said. "When asked if he did shake [the baby] too hard, Jeffrey Davis nodded his head in acknowledgment and cried."