Mr Bridges went to court armed with a psychological report which predicted Robertson had a "high risk of further sexual offending following release from prison" if he didn't undertake specialist treatment.
It was thought unlikely Robertson would seek treatment, said Justice Patrick Keane, because he continued to deny the kidnapping and indecent assault on which he was convicted.
A psychiatric report weighed more in Robertson's favour, but warned he could "simply be skilfully dishonest".
Justice Keane rejected Mr Bridges' bid to hold Robertson indefinitely on preventive detention. He told Robertson: "You are not simply deemed to be a lost cause at the age of 19."
One reason Justice Keane cited was the recently granted ability by Parliament for an Extended Supervision Order to be made on release. Robertson was made the subject of one, but to no avail.
Justice Keane saw the danger in Robertson's kidnapping of the girl - a crime he had attempted with a slightly older child the day before. The judge said Robertson "accepted risk but you also planned. You were persistent. Before your offending became more serious you were interrupted."
The interruption was by Sergeant Dave Thompson, a police officer now based in Nelson. Mr Thompson was part of an escalating search for a 5-year-old lured into Robertson's car as she walked to school. Her brother, 7, had raised the alarm an hour earlier when he arrived for classes.
As police began to search with few leads, Mr Thompson followed a hunch and drove down a long, narrow, winding road into countryside behind Tauranga.
He found Robertson in his car parked on the side a remote road, near Kaiate Falls. In the car was the sobbing girl.
"She was crying and had tears rolling down her cheeks," Mr Thompson told a court in 2005. His first action was to get her away from Robertson. His second - to make sure Robertson went nowhere.
When he took the girl to safety, she told him: "That man hurt my heart."
Tony Robertson evidence transcript (app users click here)
2006 judgement (app users click here)