Peterson was shot by a police sniper several hours after the killings

The shootings on Sunday have left the small town of Crandon, in the north of the Midwestern state, in shock.

The gunman, named as Tyler Peterson, 20, worked full-time as a deputy sheriff in Forest County.

As well as his ex-girlfriend, he shot two childhood friends and a 14-year-old girl. His motive is not yet known.

Police Chief John Dennee said Peterson, who also worked as a part-time police officer, was not on duty at the time of the shooting.

The incident occurred at his ex-girlfriend's house shortly before 0300 local time (0800 GMT), where the young people had gathered to watch movies and eat pizza, reports said.

A seventh youth is said to be in critical condition in hospital.

Tight-knit community

Residents of Crandon, a community of 2,000 about 225 miles (360 kilometres) north of Milwaukee, were ordered to stay in their homes while police hunted for Peterson.

At about 3pm local time he was "brought down by a sniper", Crandon Mayor Gary Bradley said.

The young people had gathered at a house to watch late-night movies

"There is probably nobody in Crandon who is not affected by this," Mr Peters said, adding that students would be especially affected.

"They are going to wake up in shock and disbelief and a lot of pain."

Jenny Stahl, whose 14-year-old daughter Lindsay was the youngest victim, said she had thought the teenager would be safer staying at a friend's house than travelling home late at night.

"I'm waiting for somebody to wake me up right now. This is a bad, bad dream," Mrs Stahl said.

Bud Evans, an elder at Crandon Praise Chapel, told BBC News 24 that worried relatives had gathered at the church as they waited for news.

"If there's five or six children or kids, young adults, whatever, involved in this, I'd know every one of them - the community's that small and that tight-knit," Mr Evans said.

The incident comes only six months after the Virginia Tech campus shooting, in which more than 30 people were killed.