KEY POINTS:
New Zealand First leader Winston Peters says he will not be taking the Serious Fraud Office's advice and declaring another donation that contributed to his legal fees.
Mr Peters dismissed the SFO's finding that money paid to cover $14,650.37 in legal costs he incurred "may have been required
to be returned to the Registrar of Pecuniary Interests".
He cited the SFO's use of the word "may" as a weakness in its reasoning.
"Do you know the reason you use the word 'may'? Because you don't know whether you are Arthur or Martha with your legal interpretation, that's why."
Mr Peters said his view and legal advice was that there was nothing to declare.
"It is clear to me the SFO knows nothing about electoral law whatsoever."
Mr Peters was required to pay National MP David Carter $14,650.37 in legal costs in 2006. It was paid to Mr Carter in two lots of $13,640.37 and $1010.
It was covered by a donation the SFO said was made to the Spencer Trust and paid out from there. The SFO did not name the donor.
The donation is separate from the $100,000 from billionaire Owen Glenn and $40,000 from the Spencer Trust that both went toward legal costs. Mr Peters has already amended the register to show these as gifts.
The SFO found no fraud in its investigation but passed information about the David Carter legal costs to Auditor-General Kevin Brady, who audits the MPs' returns.
A spokeswoman for Mr Brady said he was assessing the information.
Meanwhile, a former assistant police commissioner is overseeing the hunt for the SFO staffer who wrote an anonymous letter bagging NZ First.
Roger Carson is working with an SFO investigator to find the letter-writer who condemned NZ First MP Ron Mark for supporting the office's abolition.
The SFO investigation into the NZ First donations controversy was launched a week after the letter - and its proposed merger with the police was put off until after the election.
Mr Peters later produced the letter as evidence of the SFO being engaged in a political action to secure its survival. He said he wanted the letter-writer found.
"If you are going to run a proper bureaucracy, you can't have people politicising the movement. They should have told us who it was by now."
Mr Carson is a retired assistant commissioner who also works for the Independent Police Conduct Authority. SFO director Grant Liddell confirmed Mr Carson would assist its internal inquiry.
Mr Liddell would not say if the letter-writer had been found, only that the inquiry was not completed.
State Services Commissioner Iain Rennie was also being kept informed.
The letter was written to Mr Mark after he voted with the Labour members of the law and order select committee to abolish the office, which has about 30 staff.
It was sent in an envelope stamped with the SFO address and made mention of other staff being aware it was written. It said Mr Mark had "destroyed" the office, and lambasted him for a lack of integrity and honesty.