The Independent Police Conduct Authority has investigated how the police handled the inquiry into John Banks' donation returns following the Super City election.
However, the findings of the IPCA will not be released publicly until the court case is finished.
The police received complaints in April 2012 alleging Mr Banks had failed to properly declare details of donations from Kim Dotcom and SkyCity as required and therefore committed a criminal offence.
Police conducted an investigation into the matter and eventually decided not to prosecute Mr Banks.
However, a private prosecution was then launched by Graeme McCready against Mr Banks and he was found guilty of filing a false electoral return in respect of the Dotcom donations.
He was convicted and sentenced to two months' community detention and 100 hours' community service.
Since then, the Court of Appeal quashed the conviction based on new evidence and ordered a retrial.
The Court of Appeal judges are now considering whether to reverse their decision to order a retrial, because of new material which the Crown failed to disclose to Mr Banks' legal team before the appeal hearing.