A young man has been sentenced to one year's home detention and 400 hours of community work for the high-speed crash that killed the granddaughter of Sir Howard Morrison.

Samuel Malcolm Griffiths pulled the handbrake while speeding on an Auckland motorway, causing the crash that killed 17-year-old Kiriana Morrison.

On February 19 last year, about 2.15am Morrison was a rear-seat passenger in one of two cars that collided on the Northwestern Motorway.

She was not wearing a seatbelt and was thrown through a window during the collision.

Advertisement

Today at the High Court at Auckland, visibly emotional friends and family filled every seat in the public gallery, including the seats normally reserved for a jury.

Her parents read victim impact statements that showed their world had been shattered by the loss of a treasured daughter.

Her mother Libby Martin said devastation would never begin to describe her feelings and she recalled the trauma of identifying her daughter at the morgue.

"It's something no parent should have to do."

Morrison's father, Richard Morrison, said she was scared of fast cars and the crash would have been a nightmare for her.

"She left this world screaming."

Crown prosecutor Mark Harborow said an aggravating factor was that the level of alcohol Griffiths had consumed was well over the limit for an adult, let alone someone aged 18.

The speed was also significant, Harborow said.

"The speed was in the range of 124km/h to 142km/h in an 80km/h zone."

Then he made probably the "most stupid decision in the world" to pull on the handbrake while travelling at that speed, Harborow said.

The car hit a barrier and crossed several lanes to the other side of the motorway where it collided with a taxi carrying passengers, he said.

Morrison was thrown through the window and was killed.

A second victim, who was also not wearing a seatbelt, suffered lacerations and a concussion in the crash.

"The alcohol, the speed and the handbrake render this case very serious."

One of the occupants, a young male, had pleaded with Griffiths not to pull the handbrake and had reached forward from the backseat to try and hold the handbrake down, Harborow said.

Griffiths was on a restricted licence and should not have been travelling at that time with passengers, he said.

Much was made in the defence case that Griffiths had ADHD and ASD but those were background factors, Harborow said.

Justice Kit Toogood said it was very clear to him that Griffiths had suffered from longstanding conditions it was "not something the defence had dragged up" to excuse appalling behaviour.

Defence lawyer Anthony G V Rogers said Griffiths had shown genuine remorse, apologising to family members and sending flowers with a card to Selwyn College for Morrison's funeral.

Rogers said Griffiths "was in tears throughout" the police interview and took full responsibility for what he did.

"I am terribly sorry for what happened, there is no excuse for what I did," he had told police.

He would do anything to go back and change it, Rogers said.

"The loss of Miss Morrison can never be matched by anything Mr Griffiths has suffered."

The episode has been a tragedy for all involved, Rogers said.

Today, Justice Kit Toogood said Griffiths had previously pleaded guilty to dangerous driving causing death and dangerous driving causing injury.

"I want to acknowledge all of those in the courtroom who are here in support of the families who have suffered, and are suffering".

Morrison's mother struggled to move on watching her daughter's peers accomplish new milestones, Justice Toogood said.

She described her as a talented, beautiful and courageous person with a "smile for everyone".

"Kiriana was right at the start of her life as a young woman."

Justice Toogood said at the time of the offence Griffiths had a alcohol reading of 587mcg of alcohol and had been unsupervised driving on a restricted driver's licence after curfew, he said.

What happened in this case is a "classic example" of why those restrictions must be imposed.

"You were guilty of an extremely dangerous manoeuvre twice, by applying the handbrake while travelling at high speed."

Lengthy heartfelt letters had been written in support of Griffiths from by his parents.

"Your parents speak of you with great love and affection."

Naturally they were very distressed by this offending, he said.

The court heard how Griffiths had ADD, ASD, Asperger syndrome and OCD.

Griffiths had been nominated as the safe driver but was only convinced to drive in the early hours of the morning, Justice Toogood said.

"That is not mere bravado, that is who you are and that is how you behaved.. because of these medical conditions."

Medical experts had spoken of the devastating effect prison would have on Griffiths even at a short term, Justice Toogood said.

To a significant degree it was the combination of youth and his personality disorders that contributed to the recklessness that caused Morrison's death, he said.

Justice Toogood said Griffiths had shown deep remorse and took full responsibility for his actions calling Morrison's mother the day following the crash to apologise.

"How difficult must that have been for you both."

Griffiths had no previous convictions.

Justice Toogood sentenced Griffiths to one year of home detention, 400 hours of community work and disqualified him from driving for six years.

For dangerous driving causing injury he would also serve six months home detention which would be served concurrently.