A sheriff's deputy who opened fire at a pizza party and killed six people reportedly flew into a rage when he was rebuffed by his former girlfriend and others at the gathering called him a "worthless pig".
A friend told the Milwaukee Journal Sentinel that Tyler Peterson, 20, visited him after the rampage and calmly explained what he had done. "He was very remorseful about what happened," said Mike Kegley.
Police said Peterson had stormed out of the party, retrieved an AR-15 rifle from his vehicle and burst back into the house, firing 30 shots. All but one of the partygoers were killed. They ranged in age from 14 to 20.
Peterson, a deputy and part-time Crandon police officer, died later after what authorities said was an exchange of gunfire with law enforcement officers. It was unclear whether Peterson was shot by police, took his own life or was wounded and then shot himself.
Mr Kegley said Peterson visited him about five hours after the rampage early on Sunday. "He wasn't running around crazy or anything. He was very, very sorry for what he did," said Mr Kegley, adding that he gave Peterson coffee and food and later made repeated calls to authorities.
Leon Stenz, the district attorney, said he talked to Peterson on the telephone for five or 10 minutes just before he died, as they tried to find a way for the killer to turn himself in. Moments later, Peterson ran toward a wooded area where he was shot, he said.
Mr Stenz said he knew Peterson quite well because he handled several cases with him. "He always seemed to be level-headed and fine during those meetings. I think he wanted to talk to me because he knows I'm fair," Mr Stenz said.
The shooting raised questions in the remote northern Wisconsin community of 2,000 of whether Peterson was qualified for his law enforcement positions. Police acknowledged Peterson received no psychological screening before being hired on 11 September 2006. His year-long probation ended last month.
No formal national standards exist for hiring police in the United States.
The six young people who died were either students or graduates of Crandon High School, where Peterson had graduated.
The lone survivor, Charlie Neitzel, 21, was still in serious condition but recovering at a hospital.Reuse content