The family of slain teenager Christie Marceau say they don't agree with her killer's insanity verdict and in their eyes "he will always be guilty".

Judge Helen Winkelmann sentenced Akshay Anand Chand, 19, to three years imprisonment on kidnapping and assault charges today, after finding him not guilty by reason of insanity on a murder charge yesterday.

Justice Winkelmann said the jail term would be served while Chand, 19, is in a psychiatric hospital, which he was confined to indefinitely yesterday.

Marceau, 18, was stabbed to death by Chand at her Hillcrest home on November 7, 2011.  Two months earlier, she had been kidnapped and assaulted by Chand, who was arrested and sent to Mt Eden prison.

Marceau's father Brian Marceau read a statement outside the High Court at Auckland today saying he could not understand how someone could be "both guilty and not guilty".

"For us no sentence will ever be sufficient for the loss of Christie. It will never bring her back or even make us feel that justice has actually been done," he said.

"We do not agree with the term 'not guilty by reason of insanity', for us he will always be Christie's murderer and in our eyes he will always be guilty."

Chand was able to be sentenced on the earlier charges because psychiatrists said at that stage he was well enough to know right from wrong.

The court heard how Chand, who knew Marceau from primary school and a supermarket job, had called her for help on September 6, saying he was going to kill himself.

Chand then hid a 20cm kitchen knife in the waistband of his pants, intending to rape her.

When Marceau arrived they sat and Chand talked about his problems while holding a knife. He asked her to remove her clothes and said,  "If you don't obey me, I'll knife you. If you scream, I'll knife you. If you try to escape, I'll knife you."

After more than half an hour, Chand decided not to rape her, and allowed her to leave.

Today, Chand's lawyer Mary-Ann Lowe said after Marceau left Chand took an overdose of pills that he believed would be fatal.

She said that gave the court an indication of his mental health. Lowe said he was suffering from "pervasive and severe" undiagnosed schizophrenia and lacked insight into his offending.

She asked the court to take that into account when sentencing, along with Chand's youth, his previous good character and his remorse.

The Crown said it was important to sentence Chand as part of his rehabilitation to instil a "sense of responsibility" in him.

"It is important to denounce the conduct which took place on that day in September," counsel said.

The Crown said Chand's purpose had been to terrify Marceau and to take vengeance on her  - because he believed she was not helping him enough - by raping her, though he did not go through with it.

The Crown did not believe remorse was a mitigating factor, because Chand had earlier expressed remorse for his own benefit - in order to get out of jail - and that needed to be considered.

Justice Winkelmann said Marceau's life had been fundamentally changed after the kidnapping. She was terrified Chand would return to hurt her, but was trying to get on with her life. Her family too had suffered, leaving them fearful and stressed.

She acknowledged Chand had been suffering a mental illness but was coherent enough not to go through with the rape, showing some moral judgement.

However, she was not satisfied he was remorseful.

Justice Winkelmann sentenced Chand to three years jail on one count of kidnap, two years for a count of assault with intent to sexually violate, and one year for the count of threatening to cause grievous bodily harm. The sentences would be served concurrently.

In the murder hearing yesterday, Justice Winkelmann ruled  that Chand would be confined indefinitely in a psychiatric ward as a special patient to protect public safety.

Winkelmann said despite the calculated nature of the killing, Chand was labouring under delusional concepts and she accepted he was insane when he murdered Marceau.

The court had heard from two psychiatrists that Chand had said voices in his head told him to kill Marceau because she was the devil.

They found, in separate diagnoses, that Chand did not know right from wrong at the time of the murder because he was suffering a "disease of the mind". He is now being treated for schizophrenia.

As a special patient, he will not be allowed free until the Minister of Health approves his release.

- © Fairfax NZ News