A gunman opened fire on a group of people outside a trailer home in Wisconsin, killing three brothers, before critically wounding himself, police said Sunday.

Menomonie Police Sgt. Andrew Crouse said a 23-year-old man from St. Paul, Minn. shot and killed the brothers and wounded another man in the western Wisconsin trailer park.

The three brothers were identified as Toua Kong, 32; Siong Kong, 25; and Seng Kong, 13. The shooting took place in front of the trailer where Siong lived. The two other brothers lived in a different trailer, Crouse said.

Police said the fourth man — identified as 25-year-old Toua Xiong, of Menomonie — was taken to an area hospital with non-life threatening wounds. Toua Xiong is not related to the brothers, police said.

Crouse said the gunman was in critical condition at an area hospital. Police believe he shot the four before turning the gun on himself.

Investigators believe the suspect knew the victims but was not related to them. Authorities do not believe the shooting was gang or drug related, and the investigation is ongoing, Crouse said.

He said neighbors in the Menomonie trailer park, located 70 miles east of Minneapolis, were in shock.

"People are upset," he said. "Right now we just want to let the families get together and grieve amongst themselves."