STILLWATER — A 28-year-old Minnesota man accused of assaulting his fiancee’s young son is now charged with murder after the boy died this weekend.

According to a press release, Jonathon Wierstad appeared in Washington County court on Monday on a second-degree murder charge. He previously had been charged with first-degree assault.

Wierstad called 911 in May to report the boy had fallen down stairs at their home in Willernie. The 16-month-old had been on life support since the incident and died Saturday.

The complaint said the child suffered a head injury resulting in massive swelling and bleeding on his brain.

Bail is set at $2.5 million without conditions. Wierstad’s attorney declined comment.

According to a press release, Wierstad earlier pleaded no contest to substantial battery of a child in Wisconsin’s St. Croix County in 2014.