Attorney-General Chris Finlayson is "taking a close look" into the prosecution of John Banks following a ruling which found the Crown misled the court.
Mr Banks was scathing of the conduct of scathing about the conduct of Crown prosecutor Paul Dacre, QC, and Solicitor-General Mike Heron, QC, following a Court of Appeal decision which acquitted him yesterday of filing a false electoral return.
"I was held to account when I was told by the judge, 'the prisoner can take his place in the dock'. I was held to account...I'm saying the Solicitor-General has a lot to answer for," Mr Banks said yesterday.
"Withholding evidence from the Court of Appeal is a serious breach of process. Having the evidence in the briefcase but, for whatever reason, not giving it to the court is a very serious error of judgment at the very least.
"We wouldn't be here today if the Court of Appeal had that new evidence in front of them last year."
A spokeswoman for Mr Heron declined to comment and Mr Dacre has not returned messages yesterday.
But the Court of Appeal - Justices Ellen France, Forrest Miller and John Wild - disagreed with the Crown's argument that the so-called "Butler memorandum" did not need to be disclosed.
"We hold rather that the Crown could not both withhold the memorandum and resist the appeal in the manner that it did. The effect was to mislead the Court," wrote Justice Miller.
"We are satisfied that there has been a serious error of process. It is, we accept, attributable to an error of judgment rather than misconduct."
Mr Finlayson, who is the Minister responsible for the Crown Law Office and appointed Mr Heron as the country's most senior Crown lawyer in 2012, was not available to be interviewed.
Asked whether he had concerns about the conduct of the Crown and retained confidence in the Solicitor General, a spokeswoman said Mr Finlayson is "taking a close look into the matter".
"He is unable to make any further comment at this time but confirms he has confidence in the Solicitor-General."
She declined to comment further when pressed about what "taking a close look" meant.
The undisclosed material which led to the Court of Appeal acquitting Mr Banks was a memorandum written by lawyer Rowan Butler who was instructed by Mr Dacre to interview Kim Dotcom about the affidavits filed by two American businessmen before the appeal hearing.
The pair said they arrived in New Zealand on June 5, 2010 and were taken to Dotcom's Coatesville mansion, where they had lunch with Mr and Mrs Banks and Dotcom and his wife Mona. Nothing about electoral donations was discussed, according to their affidavits.
This is at odds with evidence given at the trial, where the Crown contended the lunch was held on June 9, 2010 and the presence of the Americans was denied by the Dotcoms, as well as their bodyguard Wayne Tempero.
The defence was able to prove at the trial there was no lunch on June 9, because Mr Banks was campaigning and Mrs Banks was at work.
In finding Mr Banks guilty, Justice Edwin Wylie said Dotcom was a good witness but he was wrong about the date of the lunch and ruled it must have happened on June 5.
But when interviewed by Mr Butler about the new affidavits before the Court of Appeal hearing, Dotcom accepted the evidence of the US businessmen - including that donations were not discussed at the June 5 lunch. Instead, he said there was a second lunch - again on June 9 - at which the donations were discussed.
The interview with Dotcom was never disclosed to Mr Banks' legal team before the Court of Appeal hearing. The appellate judges said yesterday they would not have ordered a retrial had they been told of the Butler memorandum, so therefore there was a miscarriage of justice.