Akshay Chand was found not guilty of murdering Christie Marceau by reason of insanity - but he has never denied stabbing her to death at her North Shore home.
Today, after heavy suppression orders were lifted, his confession to police can finally be published.
And the Weekend Herald can reveal that Chand's mother had hidden the kitchen knives from him, scared he would use them to harm Christie a second time after he kidnapped her and threatened her with a knife.
Chand, who was detained indefinitely as a special patient in a psychiatric facility this week, killed Christie on November 7 last year. The 19-year-old has never spoken publicly about what he did or why.
However he gave a full account to police in the hours after Christie died in her mother's arms on the deck of their family home.
"I woke up at 6.30am. The first thing I did was get out of bed, brush my hair. I went to my closet which had my bag and of course the contents (the knife)," he told a detective.
"I sneaked out, my sister was still in bed. I listened to Up the Ladder by Radiohead."
Chand admitted he had the song on loop and listened to it until after he had killed Christie. He walked to the Marceau house, arriving about 7am and ringing the doorbell.
"Tracey opened the door, I pulled the knife out. She was extremely shocked, as you can imagine. She started screaming. I advanced.
"Christie was on the stairs, starting to panic ... I kicked her down them. She got up quicker than I would have anticipated and she ran."
Chand chased Christie through the house and out onto the the deck. He attacked her as she tried to unlatch a gate to escape.
"I stabbed her in the head and she fell on the deck. I stabbed her, a couple more times. The knife became twisted ... it became clear that I couldn't use it any more.
"I backed off and stood there for a while. Tracey ran in ... she told Christie that she loved her and everything was going to be all right."
Chand then revealed to police that his mother, Suchita, had been hiding the kitchen knives since he was released on bail. He was facing charges of kidnapping Christie and threatening her with a 20cm kitchen knife. So when he was bailed Mrs Chand decided it was safer to hide them.
"Mum hid all the knives but I guess I was one step quicker than her ... I put the knife in the bag a week before. Of course it was premeditated."
Mrs Chand has declined to speak to the Weekend Herald since her son was charged with murder in November. But she gave a statement to police.
"Whenever I left the house I would put all the knives in a compartment under the oven. There is a panel that comes off but to look at it you wouldn't know," she said.
"I would put the knives behind the panel when I wasn't home and I would bring them back out when I got home. At no time did Akshay ask where the knives were and I have no idea that he realised I was hiding them. Obviously I was concerned about what he had done to the girl previously. But, I thought he had learned his lesson.
"Over the last couple of days before the girl got killed I had been forgetting to hide the knives."
Unknown to Mrs Chand, her son had already chosen the knife he would use to kill Christie and hidden it in his bedroom.
One of Chand's bail conditions was a 24-hour curfew, meaning he could leave the house only for medical or legal appointments accompanied by his mother.
She was at work when he sneaked out and killed Christie. Her teenage daughter was home and called her when she found Chand had gone. But it was too late.
Chand's sister, said to be traumatised by her brother's actions, was also interviewed by police, saying she was "really scared" when he was bailed to live back at home with her after the first attack on Christie.
"I knew what he had done and it terrified me," she said. "I remember putting even the small knives away. We did this because we were both scared about what he might do.
"I took every opportunity to stay at friends' houses so I didn't have to be at home."
Doctor: Mental hospital can be tougher than jail
Being acquitted of murder on the basis of insanity does not mean an offender "walks free" - in fact, it means they could be locked up for much longer than they would have been if convicted and jailed.
In the case of Akshay Chand a special patient order was made, meaning he must be detained indefinitely in a hospital or secure facility.
A special patient order remains in force until the Minister of Health directs otherwise, based on detailed assessments.
It means Chand is still a "defendant" and will be held at the secure Mason Clinic in Pt Chevalier, Auckland, until he is no longer a risk to himself or the public.
The law states that any special patient ordered to be detained following acquittal on account of insanity must have their condition reviewed in a specific way.
A formal review of every defendant must be conducted "not later than three months" after the date the order is made, and then at least every six months.
In any case where the doctor in charge of the defendant believes he or she no longer needs to be detained, the "certificate of clinical review" must be sent to the Minister of Health, who decides whether to keep the patient detained.
University of Auckland professor Glynn Owens, a forensic and health psychology specialist, said special-patient orders were almost always made because the defendant presented "a significant danger to themselves and/or others".
Prison would be a much easier place than a mental institution to be detained, Professor Owens said.
"There's a clear path to release, there's not normally an expectation that one will have to take long-term medication, usually the other inmates will be easier to deal with and often there's, paradoxically, more freedom.
"I'd generally expect closer supervision in a psychiatric setting than in a prison setting."