The Maori Party says it does not know the identity of the person who offered it $250,000 before last year's election on condition that it backed a Labour-led government.
The offer was made through a third party, and a legal expert said today the police should investigate because, in his opinion, it clearly fell within the Crimes Act definition of bribery and corruption.
Maori Party president Professor Whatarangi Winiata said the person was never identified to the party.
His statement appeared to rule out the possibility of an inquiry to discover who it was, which has been suggested by the Government and the National Party.
"We do not know the name or identity of the person involved in putting forward an offer," Prof Winiata said.
"The donor remains anonymous."
Prof Winiata said the party understood there was nothing in the Electoral Act which prohibited conditional donations being offered, and that opinion was backed by a spokesman for the Electoral Commission who said the offer did not break any provisions of the Electoral Act.
But Auckland University law professor Bill Hodge said there was a section of the Crimes Act which said people should not offer money to MPs in an attempt to influence their actions.
"It's pretty squarely in that section," he said.
"I think there's more than enough for police to go and make their inquiries."
Party co-leader Tariana Turia revealed the offer yesterday, saying it was not accepted.
"It would have gone against basically everything we had discussed with our constituency -- where we had said we would go back to them to make the decision about who we went with," she said.
After the election, the Maori Party decided it would not back either of the main parties.
Labour has denied any knowledge of the offer, and president Mike Williams told NZPA it did not come from expatriate billionaire Owen Glenn.
There had been speculation that Mr Glenn was the mystery man because he donated $300,000 to Labour in 2005.
But Mr Williams said he had spoken to Mr Glenn, who is in London, and Mr Glenn had said he had never met Mrs Turia and did not know who she was.
"As far as he is concerned, it is either someone else or it is fantasy," Mr Williams said.
The offer was revealed as political parties remain embroiled in an election spending row.
Among the accusations are that Labour's spending on its election pledge card was unlawful, and that National covered up large donations through secret trusts.