Investigations are continuing into what motivated a young sheriff's deputy to shoot dead his ex-girlfriend and five others in the US state of Wisconsin.
Peterson's family gave a statement apologising to the victims' families
Police confirmed Tyler Peterson, 20, had been in an argument with the group before he burst into the home where they had gathered and fired 30 rounds.
He fled but said he was the shooter in phone calls with police, and later died when talks on his surrender failed.
The killings have shocked the town of Crandon, in the north of Wisconsin.
As well as his ex-girlfriend, Peterson's victims included two childhood friends and a 14-year-old girl.
A seventh youth, who is said to be in a serious but improving condition in hospital, has been interviewed by police.
Peterson was off-duty at the time of the shootings.
'No longer a cop'
Speaking at a news conference, the authorities confirmed that Peterson had previously been in a relationship of a few years with one of the victims.
The young people had gathered at a house to watch late-night movies
They said investigations into his motives for opening fire at the house shortly before 0300 local time (0800 GMT) on Sunday were continuing.
Peterson, who worked full-time as a deputy sheriff in Forest County and part-time as a police officer in Crandon, had undergone the usual background checks, officials said.
"We had no idea, obviously, that anything like this would ever occur," said Crandon Police Chief John Dennee.
"Once we realised that he was our suspect, he was no longer a cop."
The rifle Peterson fired was of the type used by the sheriff's department but it is not yet known if it was the one issued to him as a law enforcement officer.
'Shock and disbelief'
Police have not yet confirmed the cause of Peterson's death. The mayor of Crandon earlier said he had been shot by a police sniper.
Residents of Crandon, a community of 2,000 about 225 miles (360km) north of Milwaukee, were ordered to stay in their homes while police hunted for Peterson.
Having fled after firing at the first police officer on the scene, he was tracked down on Sunday afternoon, officials said. He died after shots were fired by both himself and law enforcement officials.
"We attempted to resolve the situation by him surrendering but it was unsuccessful," said Mr Dennee. "When I spoke to him on the phone he was calm and understood the dilemma he was in."
In a statement, Peterson's family apologised to relatives and friends of the victims for their loss.
"We feel a tremendous amount of guilt and shame for the acts Tyler committed," the statement said.
"Like those close to Tyler we are in shock and disbelief that he would so such terrible things. This was not the Tyler we knew and loved."
Schools in Crandon are closed until Wednesday. Counselling has been provided for students and staff.
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," Mr Peters said.
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.