Current Crown minister and former Crown prosecutor Simon Bridges tried to have Robertson locked up permanently. The law required the High Court's Justice Patrick Keane to consider five points:
• Whether there a pattern of offending
• How seriously the community was harmed
• Whether there was evidence showing Robertson was inclined to commit serious offences in the future
• If there were signs of a lack of intent to address the lawbreaking which brought him to court
• Whether a long but finite sentence would adequately safeguard the community.
The judge considered there was a pattern of offending with serious potential for community harm. The issue, he said, was whether there was evidence Robertson would offend when released.
On this point, he said evidence was divided. Psychologists predicted Robertson to be of high risk while psychiatrists rated him as low-risk with no diagnosable psychiatric disorder.
The judge's decision turned on there being no history of "diverse sexual offending" and that it was "impossible" to predict how Robertson would be when he matured having been 18 at the time of the abduction.
Justice Keane said a far more serious case had been set aside on appeal because the court had the power to impose an Extended Supervision Order (ESO) on release and therefore didn't need to impose preventive detention. ESOs are periods of scrutiny lasting up to a decade.
It is also worth considering that Robertson was sentenced for the abduction in 2006 - four years after Parliament lowered the minimum age for preventive detention from 20 to 18. Locking teenagers away, potentially forever, is unusual.
3. Why was he released near a school?
Corrections is well aware of the difficulty putting any convicted sex offender in any community, says Northern deputy regional commissioner Alastair Riach. In Auckland, it is particularly difficult. "It's very hard in Auckland to find somewhere that's not within a kilometre of a school."
Also, there was overwhelming research showing placement of offenders in the community was a major influence in rehabilitation and reducing offending. Inmates released and isolated were a greater danger.
4. Couldn't Robertson be forced to take corrective courses inside?
Corrections repeatedly pushed Robertson towards courses, including specialist courses aimed at sex offenders. He refused to participate in any activity which acknowledged his sexual offending. His refusal played a large part in Robertson being repeatedly refused parole and being forced to serve his entire sentence.
5. Was he constantly watched by GPS monitoring?
The GPS bracelet fed real-time information to Corrections which was matched against a profile specifically developed around his release conditions. Corrections staff had marked out school and playground boundaries on computers which triggered an alarm if the GPS bracelet went into those areas. On the one occasion it did, about six weeks after his release, Robertson was telephoned inside two minutes to be told to move. He didn't answer so police were notified, leading to his arrest inside 45 minutes.
6. Why not watch him 24 hours a day?
Cost and practicality. A 24/7 surveillance of Robertson would have required a dedicated team operating in three shifts across the week, plus holiday and weekend cover. With a junior Corrections officer earning $45,000 - and the need to provide facilities where an inmate could be monitored - the cost quickly spirals towards $1m, and that's just for Robertson. There are about 140 people subject to ESOs - down from a peak of 242 - a potential taxpayer burden of more than $200m. Having said that, some inmates in exceptional circumstances can be subjected to intensive monitoring under new ESO laws. Inmates who qualify are those with learning disorders, low IQ and deviant sexual behaviours exhibited from a young age. Robertson would not have met the conditions - and if he did, then so would many others also released into the community.
7. Couldn't his parole have been cancelled?
He wasn't actually on parole because he had served his full sentence. The best the Parole Board could have done was put in place strict release conditions which last for six months and bolster those by going to court to seek an ESO so he could be GPS-tagged and watched for a decade. As GPS technology has improved, this has been increasingly used in cases of inmates who have served their full sentences. By virtue of not qualifying for parole, they identify themselves as high-risk and needing special focus.
8. Why did the ESO take six months to come into effect?
Corrections applied for the ESO when it became clear Robertson was going to be released. It was granted two months after he was out, during which time he was covered by release conditions which had almost exactly the same protections built in as would be provided by the ESO. The only difference was the ESO would have extended his curfew across school hours - and Robertson's attack was against an adult.
9. Why didn't Probation Service staff check on him more often?
It did - or at least more often than it usually checks on inmates. There were 38 meetings in the five months he was out, not counting the five weeks Robertson went back inside for breaching release conditions. Frequency increased after the breach and included nine visits at his home to get a better insight into his risk level.
10. Is he going to be let out again?
His sentencing is not until August but it has been signalled that the Crown will seek preventive detention. It is extremely likely that will be granted, given the conditions outlined above in point 2. Although the sentence is indefinite, it doesn't mean he's going away forever, with the average length of sentence served by an inmate on preventive detention being about 12 years. In those cases, the Parole Board would have required the person to take major steps to address the causes of their offending. Robertson has never been able to accept the sexual aspect of his offending.
