Outside court Detective Sergeant Mark Loper said over $3 million was still missing.
He said police did not know what Gao had been doing since he left the country.
Mr Loper said Gao had been co-operative on the flight back to New Zealand.
Gao and his former partner, Kara Hurring, are accused of transferring more than $6 million of Westpac's money into several accounts before fleeing the country.
A $10 million overdraft facility was mistakenly loaded onto his Rotorua business account by a Westpac staff member.
His disappearance sparked an international manhunt involving Interpol and other overseas agencies.
Kara Hurring, 32, Gao's partner when he fled New Zealand, was arrested on related charges when she re-entered New Zealand earlier this year and is due to stand trial in February.
It is alleged that the man transferred $6,782,000 of the money into other accounts, and then both left New Zealand for Hong Kong - the man on 29 April 2009 and Ms Hurring on 3 May.
The error was discovered on May 5, with approximately half of the money recovered from New Zealand accounts, leaving an outstanding sum of $3,872,000 unrecovered.
New Zealand police received notification in the first week of December that extradition approval had been granted for Gao by Hong Kong authorities.
New Zealand police understand that Gao did not contest the extradition.
Two detectives travelled to Hong Kong last weekend to complete the process and accompany the man back to New Zealand in police custody.
The team arrived back into New Zealand at 11:30am today.
The officer in charge of the investigation, Detective Inspector Mark Loper, says today's developments were satisfying for the investigation team.
"However, there is still a great deal of work to be done to ensure that people are held accountable for this substantial theft."
- NZ Herald staff
