A former maths and economics teacher at one of Auckland's top schools funded a gambling addiction by getting credit cards in the name of a missing man and running up thousands of dollars in debt.

Photo: AFP

Rafe Callum Fannin appeared in the Auckland District Court today, where he was sentenced to nine months' home detention after earlier admitting charges of obtaining by deception and using a document for pecuniary advantage.

Judge David Harvey described the crimes as identity theft.

Fannin - who worked as a maths and economics teacher at Auckland Grammar - used Facebook to get the date of birth and name of Jamie Stephen Herdman, who disappeared in the Australian Northern Territory back in 2006.

He initially used Mr Herdman's details to get a driver's licence but, instead of a photo of Mr Herdman, he included one of himself.

The 36-year-old then applied to a number of banks and got credit cards, which he used to run up thousands in debt.

Judge Harvey said it was calculated offending that involved a significant amount of pre-meditation.

There was also a level of self-deception, he said, with Fannin telling himself he was just borrowing the money and would one day pay it back with his winnings.

The judge said, when it came to intelligence, Fannin was by no means a babe in the woods.

He said he would have been well aware that, when it came to gambling, the house always won.

Fannin also used the identities of his work colleagues.

He used the drivers' licences of two teachers he worked with and racked up thousands more in their names.

In total, he notched up $67,408 in debt.

Judge Harvey has ordered him to pay the money back.

Fannin was able to pay a lump sum of $1500 and $20 a week after that, because he was still supporting his wife and three children.

That meant the debt would not be paid off until the year 2078, by which time Fannin would be 99 years old.

Fannin still held a teaching certificate but was no longer working at Auckland Grammar and would serve his home detention in Whangarei.