CRANDON, Wis. — An off-duty sheriff’s deputy went on a shooting rampage at a home early yesterday in northern Wisconsin, killing six people and injuring a seventh before authorities fatally shot him, officials said.

The suspect was 20 years old and worked full-time as a Forest County deputy sheriff and part-time as a Crandon police officer, Sheriff Keith Van Cleve said. He would not release the suspect’s name but said he was not working at the time of the shooting.

A seventh shooting victim was in critical condition at a hospital in nearby Marshfield, Police Chief John 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 Mr. Van Cleve would not confirm that officers shot the suspect. It wasn’t immediately clear what the suspect’s motive was. The shooting occurred in a white, two-story duplex about a block from downtown Crandon.

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

The State Patrol and the Crandon Fire Department detoured a steady stream of traffic from two blocks of U.S. Highway 8 in the downtown area. Some residents stood in nearby front yards.

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.”

Then she heard eight louder shots and tires squealing, she said. “I was just about to get up and call it in, and I heard sirens,” she said. “There’s never been a tragedy like this here. There’s been individual incidents, but nothing of this magnitude.”

The sheriff said he would meet with state Attorney General J.B. Van Hollen this morning to discuss the case. Mr. Dennee said the state Department of Criminal Investigation will handle the case because the suspect was a deputy and officer.