Serious Fraud Office director Grant Liddell handed over evidence about New Zealand First leader Winston Peters to Parliament's privilege's committee because he believed it had been given misleading information.
The SFO evidence contradicted the explanation Mr Peters and his lawyer, Brian Henry, gave to the committee about how a $40,000 debt of Mr Peters' was paid.
The committee's report shows Mr Liddell approached it after considering "my responsibility as head of a law enforcement agency where I have information that is relevant to possible breach of the laws of New Zealand".
The $40,000 was the court costs Mr Peters was ordered to pay after his unsuccessful election petition against National's Bob Clarkson in 2005.
Mr Henry initially told the committee he had paid the costs - which would have constituted a gift that Mr Peters should have declared on the MPs' register of pecuniary interests.
Mr Peters told the committee he believed he had paid the $40,000.
Mr Henry then clarified in writing that he paid the costs but was reimbursed shortly afterwards by Mr Peters.
The SFO evidence showed that Mr Henry was paid by the Spencer Trust, which got the money from a donor the fraud office did not identify.
Mr Liddell wrote to the committee saying the explanation it was given, as reported in the media, was "misleading, or at the very least incomplete".
He handed over the evidence believing it was relevant to the privileges committee, which was considering whether Mr Peters should have declared a $100,000 donation from Owen Glenn on the register.
Mr Liddell said the $40,000 was not declared on the register, and was therefore a possible breach of Parliament's standing orders which were "part of the laws of New Zealand".
The committee's report said it was "surprised" to get the SFO evidence in view of the earlier explanation from Mr Peters and Mr Henry.
The committee said it did not want to comment on the $40,000 because it did not fit its narrow brief of dealing with the Glenn donation.
The committee did note that if payments were made by a third party, they constituted a gift or discharge of a debt for the purposes of the register.
The report shows Mr Liddell got the Auditor-General's recommendation before going to the committee. He also consulted Parliament's clerk.
Deputy Prime Minister and Attorney-General Michael Cullen refused to express confidence in him after he went to the committee last week.
Prime Minister Helen Clark yesterday expressed confidence in Mr Liddell's integrity - but not in his judgment.
"I have confidence in Mr Liddell's integrity, as does his minister, Dr Cullen," she said.
"The issue on which both Dr Cullen and I have refrained from comment is the issue of judgment around the approach to the privileges committee."
The Prime Minister said the issue was that Mr Liddell had not sought Crown Law's advice "which would be the normal course".
NZ First laid a complaint with the police yesterday, which alleges the SFO broke the law by handing over the information.
The party is referring to a section of the Serious Fraud Office Act, which says every member of the SFO "shall observe the strictest secrecy".
A fine of up to $5000 can be imposed for any breaches.
But the act also allows the director the discretion to disclose information "to any person who he is satisfied has a proper interest in receiving such information".