Inland Revenue says it was not the source of leaked information about NZ First leader Winston Peters' superannuation overpayments.
Mr Peters confessed late last month to repaying superannuation overpaid to him over a seven-year period from 2010 to July this year.
He made the admission after being contacted by reporters who received an anonymous tip-off, later discovering a number of government ministers and the prime minister's chief of staff had also been made aware.
Inland Revenue launched its own investigation after a claim by a reporter, later withdrawn, that it was the source.
"Our investigation has found that IR does not hold the information that became public in relation to Mr Peters' National Superannuation payments, and therefore could not have been the source," the organisation said in a statement on Tuesday.
Mr Peters has promised "serious action" against those involved in the leaks and his lawyer is understood to be investigating.
He has described being "aghast" at being made aware of the error, understood to have been a small fortnightly overpayment at the single person's rate, rather than the rate that applied given he lives with is partner Jan Trotman.
The Ministry of Social Development is also investigating whether someone within the department was behind the leaks.
Deputy Prime Minsiter Paula Bennett, as State Services Minister, and Social Development Minister Anne Tolley had both been notified by the heads of their respective departments about Mr Peters' overpayments under the "no surprises" rule.
Ms Tolley also notified Wayne Eagleson, chief of staff to Prime Minister Bill English.
Mr English has said he believes the leaks did not come from within the Beehive or the National Party, and has admitted given the confidential nature of the information it would have been better for the ministers not to have been notified.