Dr Chaikin said he had seen the memo obtained by ABC TV.
"I would rate it as a smoking gun because of the nature of the warnings," the former adviser to the attorney-general's department told ABC TV on Tuesday.
"These are clear warning signs of corruption."
A committal hearing in Melbourne last week heard that eight former executives of the wholly RBA-owned NPA and the part-owned Securency were involved in a conspiracy to bribe public officials at foreign banks in a bid to secure contracts to make plastic banknotes.
The scandal was exposed in the media in mid-2009.
But ABC TV reported on Tuesday then NPA company secretary Brian Hood detailed corruption concerns in the mid-2007 memo to Mr Battellino.
Dr Chaikin says the RBA should have called in the police after it received the memo.
It was "incredible" that RBA governor Glenn Stevens told a parliamentary hearing in 2011 that the bank didn't know anything about the scandal before it was reported in the media, he said.
"It would have been the most extraordinary thing in the public service for the governor of the Reserve Bank not to be told about this memo," the corruption expert said, adding it appeared there'd been an orchestrated attempt to cover up the truth.
"A royal commission would be the only way that we have in Australia to uncover that.
"This is about what the Reserve Bank of Australian knew about that corruption and it goes to the question of the integrity of the most important financial body in Australia."
Transparency International Australia said in early August that the RBA's behaviour in the case was "tantamount to a cover-up".
"We do believe that it was incumbent upon them to report promptly any credible evidence of the sort that seems to have emerged," executive director Michael Ahrens told a parliamentary inquiry.
The RBA has been criticised for referring the allegations to a law firm before referring them to the police.
22 Aug 2012