The Riverhead quarry attacker and repeat rapist will likely die behind bars.

Photo: Stuff

Sixty-year-old Colin Jack Mitchell was today sentenced to preventive detention with a minimum non-parole period of 10 years. The sentence means he cannot be released until he proves he is no longer a threat to society.

Mitchell has bladder cancer and continues to deny his offending. His refusal to take responsibility means he will not be able to take part in rehabilitation courses while inside prison - making him an unlikely candidate for parole.

Colin Jack Mitchell had gloves, a mask and a pool cue in the back of his car when he left his Onehunga flat in the early hours of 26 February last year.

He was planning a sexual attack - and it wasn't his first.

Justice Fitzgerald said Mitchell drove into town and found a young drunk woman walking by herself. He got her into his car and drove her to a quarry in Riverhead, north-west of Auckland.

"The first memory she has of these events is coming to find herself in the quarry, wearing only her underwear, with you standing over her, in your mask."

The victim touched her head and it was bleeding. Mitchell began shouting orders at her and she managed to scramble away to call police.

CCTV cameras in town showed a car matching Mitchells had been in the area when the victim was picked up and the same car was caught on cameras at the quarry site.

The police also found gloves at the scene. One of them had Mitchell's DNA inside them.

Mitchell's explanation that he had only tried on the gloves in a shop was rejected by the jury.

They also linked him to a previously unsolved rape from 1992.

Mitchell picked a woman up as she walked home and dropped her on Rosebank Rd in the Auckland suburb of Avondale.

"You ambushed her from a hiding place behind a tree," Justice Fitzgerald said.

"You punched her in the face and in the head, enough to stun her, but not to drop her, and then you put her in a head lock."

He dragged her down a driveway behind a factory and raped her.

Mitchell claimed the sex was consensual - a story the jury did not believe.

He also has convictions for the rape of a sex worker in 1985 whom he threatened with violence.

Justice Fitzgerald said two experienced health assessors found Mitchell was a high risk of re-offending.

"In my view, there is a clear and disturbing pattern of serious sexual offending by you, over a period of some decades. Having considered your full offending history, there is also a clear similarity between the nature of your offending, including its predatory nature, offending against strangers, seeking out vulnerable victims, associated violence, threats of further violence if instructions are not carried out, and in more recent times, removal of your victims to remote locations to prevent detection."

Mitchell told one health assessor he didn't see any point in taking part in rehabilitation for sex offenders.

Justice Fitzgerald said Mitchell posed a serious risk to the community and his advancing age had not made him safer.

He remained stoney faced as the victim read out a suppressed victim impact statement and Justice Fitzgerald passed sentence.

Outside court, Detective Senior Sergeant Kim Libby paid tribute to Mitchell's victims who showed strength and courage.

"One of these victims has spent 25 years looking over her shoulder without being able to get any closure. While sentencing today does not mean that pain will go away, hopefully it will provide her with some level of comfort."

Mr Libby said the incident in Riverhead had dramatic effects on the Rodney and Riverhead community.