One of the fatalities is, according to Madison's police chief Shon Barnes, the suspected perpetrator, who was a teenage student at the school.
The other two confirmed fatalities are a teenage student and a teacher at the school. Six people were taken to hospital after the shooting, and two of them have, according to the police chief, life-threatening injuries.
It's a day of sorrow, not just in Madison but throughout the entire USA, he says according to NBC News.
According to local media, nearly 400 children from preschool to the final year of elementary school attend the affected school in Madison, the state capital.
According to CNN, Monday's shooting is the 83rd in 2024.