Westpac's botched attempt to recover its losses through the Hong Kong courts mean its runaway millionaires are a step closer to keeping the cash.
Rotorua couple Leo Gao and Kara Hurring skipped the country for Hong Kong in May after Westpac mistakenly put $10 million into Mr Gao's account.
Mr Gao had asked for a $100,000 overdraft.
Westpac said most of the money had been recovered but $3.8 million was still outstanding.
Police are seeking the help of Chinese authorities to find the pair.
If New Zealand police can convince Chinese authorities to extradite the runaways, then Westpac might have a chance of recovering the remaining $3.8 million.
Even then, Gao would have to agree to hand over the money to avoid facing a harsher penalty, the Herald on Sunday reported.
Westpac has confiscated and sold Gao's property investments for below-market value to recover its losses and settle an employment dispute with the worker responsible for making the mistake.
The bank lost its court case in the Hong Kong after trying to recoup money Gao passed through a casino in nearby Macau.
It has to pay the casino's legal bills, and details of the case are contained in a legal judgment from the Hong Kong Court of First Instance.
Deputy High Court Judge Ian Carlson, described how Gao was "quick to take advantage" of the error, in his ruling.
Mr Carlson believed Gao had transferred "ill-gotten funds" to "various accounts in Mainland China and Hong Kong".
His ruling revealed that Gao's brother Lei Gao, along with his mother and business partner Huang Di Zhang, helped him transfer the money.
One of the accounts into which Gao deposited money was with Wynn International Marketing, a casino and resort operator with a casino in Macau, Carlson said.
The ruling reveals that Gao transferred only part of the missing millions to the casino -- $658,643 -- but he is the only person named in legal action by Westpac in the Hong Kong courts.
This suggests the bank does not know where the rest of the money is.
NZPA