"I am satisfied that Mr Robertson poses a very considerable risk indeed," he said in his judgment last week.
"I consider that it is likely that he will commit an indecency on a child under the age of 12 years, and that he will abduct a child for the purpose of sexual connection.
"The evidence compels the conclusion that (he) is impulsive, and that he is unable to control his anger and aggression. Mr Robertson has a predilection for, and a proclivity towards, sexual offending. He has shown no remorse ... Indeed, he continues to deny it."
Robertson was released on December 11 last year, three days before his statutory release date.
He breached his release conditions twice within five weeks of that release.
He appeared in the North Shore District Court last month charged with the first breach for hosting a visitor overnight at his Parole Board-approved accommodation and pleaded guilty. He was sentenced to two months' imprisonment.
He has a scheduled hearing this month for the second breach for visiting a park, "where children were likely to congregate".
A Corrections spokeswoman said extended supervision orders allowed Corrections to monitor high-risk child sex offenders for up to 10 years after release.
"This means a person subject to an ESO will have to report to their probation officer regularly ..."
She said they could also be subject to electronic monitoring, GPS and restrictions on where they can live.