STILLWATER, Minn. - Months after pleading no contest to a child abuse charge, a Washington County man is now accused of murdering a 16-month-old boy.

Jonathon Wierstad, 28, of Willernie, has been charged with second-degree murder.

According to the criminal complaint, officers were called to Wierstad's home on May 11th for an unresponsive child. Officers arrived to discover an ambulance had rushed the child to Gillette Children's where he underwent emergency brain surgery. The charges state the boy suffered a "closed head injury" that resulted in "massive swelling and bleeding on his brain." The swelling was so severe, doctors had to remove part of his skull.

According to the complaint, investigators questioned Wierstad who told them he watched the boy as his fiance left to pick up her older son. While she was gone, Wierstad reported he walked down the stairs and forgot to close the baby gate. A short time later he said he heard a thud and claimed to find the boy lying at the bottom of the stairs.

The surgeon who worked on the victim concluded the boy's injuries were not consistent with a fall down stairs. The boy died June 3rd as a result of the injuries suffered on May 11th.

According to the charges, Wierstad is currently on felony probation in St. Croix County, Wisconsin after pleading no contest to causing permanent brain damage to his then girlfriend's three-year-old son.

If convicted, Wierstad faces up to 40 years in prison.