As Tony Robertson is sent to jail for "life", the man who put him away for his previous offending against children has described the killer as "incredibly cold and angry".

Transport Minister and former Tauranga Crown prosecutor MP Simon Bridges has finally spoken about the man he helped send to prison in 2006.

Photo by David White. Fairfax NZ.

Simon had appealed at the time for Robertson to be sentenced to preventive detention, but the sentencing judge in 2006 showed leniency to the then-teenaged Robertson.

Speaking after Robertson was sentenced on Thursday for the rape and murder of Blessie Gotingco, Simon recalled the 2006 case as "haunting".

"I recall Robertson himself as an incredibly cold and angry individual. His yelling and swearing in the witness box led me to seek additional security at court, something I never did in any other case.

"Prosecuting the Robertson case in 2006 was a haunting experience both because of the circumstances and the offender.

"The five-year-old victim's evidence that she was 'stolen' on her walk to school, along with the circumstances in which the police found her with Robertson, was chilling.

"I believe Robertson is one of New Zealand's worst offenders and I am glad justice has taken its course."

Earlier on Thursday, Robertson, now 28, was sentenced to preventive detention for the rape and murder of the Auckland mother.

He may never leave prison.

Justice Timothy Brewer told Robertson at sentencing: "You came across Mrs Gotingco, a small, slightly built woman who was crossing the road. You took advantage of the opportunity and deliberately ran her down.

"It was a bestial action and it was committed with the intention that your victim would not survive."

Justice Brewer noted that Gotingco was badly hurt after she was struck by Roberston's BMW.

"You did not seek treatment. You put her in your car and drove to your garage. You raped her in the back of your car, despite her injuries. You strangled her with your hand, I infer to subdue her. After you had raped Mrs Gotingco you killed her with a knife. This was so she could not identify you. You stabbed her many times before cutting her throat."

Brewer had no doubt Robertson would reoffend, given the chance.

"Your history, and the reports I have received, make it very plain that you would be likely to commit another qualifying offence no matter how long any finite sentence might be," he said.

On the charge of murder, Robertson was sentenced to life with a minimum non-parole period of 24 years.

He was sentenced to preventive detention on the rape charge.

The sentence, delivered in the High Court at Auckland meant Robertson may be locked up indefinitely.

The court's gallery was packed with members of the public and members of Gotingco's family.

Robertson was flanked by five guards, and sat with his head bowed.

In a victim impact statement that was read to the court, Blessie's husband Antonio said their lives would never be the same again.

"Our dreams have been turned into a recurring nightmare quite literally."

Their dream of buying a home was now gone, and his very will to live had suffered.

"It makes me so angry knowing Blessie was living a healthy and happy life, and did nothing to this offender to deserved such an unbelievably violent cruel, depraved vicious and callous attack.

'This offender still has his life. No one has the right to do the evil that was inflicted on my wife, and I pray that he never has the opportunity to do this again.

"Words cannot express the pain, torture and anguish my family has endured."

Blessie's son John Gotingco told the court his mother was "the greatest person I know”.

"We had so many hopes and dreams, dreams that will now forever remain dreams.

"Not a day goes by when I don't think of the events of May 24. They are forever in my thoughts."

Outside the court, family friend Alan Wharerau said the Gotingcos were relieved the "cowardly and evil" Robertson was behind bars.

"While no sentence can return Blessie to us, the legal process is now completed and we can focus on our family once again."

Wharerau described Blessie's death as "preventable" and said he hoped it would at least serve as a catalyst for change.

"There are other Robertsons living within our communities and the family is hopeful the independent review's scope will ensure that their monitoring capabilities and processes of the Corrections department are reviewed and corrected urgently. Blessie's death must not be in vain.

"Now that this sentence has been passed down Robertson will never walk the streets again."

Robertson, 28, whose name was suppressed during his trial and appeal, was convicted of the 2014 rape and murder in May.

Crown prosecutor Michael Walker said the crime was premeditated.

"Robertson planned to abduct, rape and kill the only witness to his crime."

The impact on Blessie's family was "incalculable" he said.