CRANDON, Wis. – An off-duty sheriff’s deputy went on a shooting rampage early yesterday at a home where seven young people had gathered for pizza and movies, killing six and critically injuring the other before authorities took him down, officials said.

The gunman, Tyler Peterson, was 20 years old and worked full-time as a Forest County deputy sheriff and part-time as a Crandon police officer, said Police Chief John Dennee.

Three of the victims were students at the small town’s high school, and three were recent graduates, a school official said. The gunman may have graduated from the same high school.

Peterson was not working at the time of the shooting, Sheriff Keith Van Cleve said.

The survivor was hospitalized in nearby Marshfield, Dennee said. A Crandon police officer who fired back was treated for minor injuries and released.

Gary Bradley, mayor of the city of about 2,000, said earlier yesterday that the suspect had been brought down by a sniper, but Van Cleve would not confirm that officers shot the suspect.

It wasn’t immediately clear what the gunman’s motive was, but the mother of a 14-year-old victim said the suspect may have been a jealous boyfriend. The shooting occurred in a white, two-story duplex about a block from downtown Crandon.

“It was a pizza and movie party,” Dennee said.

Three of the victims were Crandon High School students, said schools Superintendent Richard Peters, and the other three had graduated within the past three years.

“There is probably nobody in Crandon who is not affected by this,” Peters said, adding that students would be especially affected. “They are going to wake up in shock and disbelief and a lot of pain.”

Peters did not know whether Peterson had also graduated from the 300-student high school. But Crandon resident Karly Johnson, 16, said that she knew the gunman and that he had helped her in a tech education class.

“He graduated with my brother,” she said. “He was nice. He was an average guy. Normal. You wouldn’t think he could do that.”

One of the dead was 14-year-old Lindsey Stahl, said her mother, Jenny Stahl, 39.

She said her daughter called her Saturday night and asked whether she could sleep over at a friend’s house. Jenny Stahl agreed.

“I’m waiting for somebody to wake me up right now. This is a bad, bad dream,” the weeping mother said. “All I heard it was a jealous boyfriend and he went berserk. He took them all out.”

Marci Franz, 35, who lives two houses south of the duplex, said gunshots awoke her.

“I heard probably five or six shots, a short pause and then five or six more,” she said. “I wasn’t sure if it was gunfire initially. I thought some kids were messing around and hitting a nearby metal building.”