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.

 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.

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 says 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.

The St. Paul Pioneer Press (http://bit.ly/2qYWo2R ) reports Wierstad earlier pleaded no contest to substantial battery of a child in Wisconsin's St. Croix County in 2014.