A young man has been jailed over his homicidal rage which left three members of a family dead.

Jason Alexander Downie, 20, has been sentenced to at least 35 years by the South Australian Supreme Court for the frenzied stabbing attack on teenager Chantelle Rowe, 16, and her parents in their home at Kapunda, north of Adelaide, in November 2010.

Downie, then 18, stabbed Chantelle about 35 times and raped her.

The girl's father Andrew, 45, was stabbed 29 times and the tip of a knife was later found in his skull.

Her mother Rose, 44, was stabbed at least 50 times and part of the knife was also found lodged in her skull tissue.

The Rowe family's only survivor was son and brother of the victims, Christopher, who was on holiday in Queensland when his family was murdered.

Sally Rowe: "I hope he goes to hell"

On Tuesday, setting the non-parole period, Justice John Sulan told the young killer his crimes were chilling and truly horrific.

"To describe the attack on these victims as a savage attack does not adequately describe what happened in that house," he told Downie.

"The evidence satisfies me that you went there to satisfy your desire to have a sexual relationship with Chantelle Rowe.

"It is unclear what exactly happened but it resulted in the deaths of three innocent people in their own home. The enormity of your crimes cannot be diminished.

"The consequences of your conduct in the community of Kapunda will last forever."

Justice Sulan gave a sentence discount of seven years for the guilty pleas.

Downie will be in his 50s before he has any prospect of release.

Justice Sulan said Downie had joined the grieving friends and relatives at the murder scene after the crime was uncovered.

He said Downie kept maintaining his innocence to his mother and brother even after entering guilty pleas in court.

"You seem to have been in denial," he said.

"Your pleas only came after it was clear the evidence against you was overwhelming.

"It is clear the Rowe family was a very loved family and your crime has had and will continue to have lasting effects on all of them."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 32 seconds 1 m 32 s Relatives abuse triple killer during sentencing ( Candice Marcus )

Infatuation

The court had been told Downie was a quiet and weedy teenager who became consumed by a jealousy, which turned into homicidal rage.

It was told he had a sexual infatuation with Chantelle Rowe, who was dating one of his friends.

Director of Public Prosecutions (DPP) Stephen Pallaras told the court of the horrific scene in the Harriet Street home after the killings.

"It is no exaggeration to say the hallway and floors throughout the house were covered in blood," he told the court.

"It appears from the position of the bodies of Andrew and Rose Rowe and the positioning of their blood that, even after he had stabbed them and attempted to clean up their blood, he went back to them and stabbed them again."

A defence lawyer told the court Downie was an immature young man who could not have been aware that he was capable of such violence.

The young killer wrote a letter of apology to the victims' family, but surviving son and brother, Christopher, told the court the crime had left him feeling empty.

The judge was also told Downie's own family had been shocked by the nature of the crime.

More than 100 family and friends of the Rowe family were in the courtroom as the young killer was sentenced.

One of the relatives, Sally Rowe, spoke of their heartbreak as she emerged from the court.

"I'm devastated," she said.

Chantelle and her parents Andrew and Rose were stabbed repeatedly

"He should have got a lot longer. I hope he goes to hell."

Another relative Kylie Duffield read a statement from Christopher Rowe as he stood silently at her side outside the court.

"All we can be thankful of today is that we have escaped the pain of a trial," she read.

"We can close this chapter now and I can start to focus my strength on keeping my mum, dad and Channy's memories alive and I can slowly try to find my own way to survive through this.

"Many feel my family and I have reached some form of justice today. I disagree. [That] the lives of my dad, mum and sister were viciously taken by someone of sound mind qualifies this bastard Jason Downie to only 35 years non-parole whilst my family and I continue to serve life. Please explain to me the justice in this.

"This is not a justifiable offence. He can not return my family to me so why should he have the right to any definition of life?"

Detective Superintendant Grant Moyle conceded no sentence could be long enough to compensate family and friends for their loss.

"I don't think any sentence ever was going to fully address the viciousness of this crime," he told reporters.

"Nonetheless, 35 years is a long time.

"He's facing now his 21st, his 30th, his 40th and his 50th birthday in prison.

"It'll never bring back the three Rowe members but nonetheless it's a closure for the family at this point of time."

He said the crime scene would give investigators and the person who first found the victims nightmares for a very long time.

DPP Stephen Pallaras gave his thoughts on the verdict.

"Today was the beginning of a long road for the family ... beginning of a long road of adjustment, beginning of a long road of mourning and hopefully of healing," he said.

"A 35-year sentence will certainly give Mr Downie a very long time to contemplate the sanctity of human life."

Mr Pallaras said he hoped the town of Kapunda could now start its own process of healing.