For the claim to proceed, Mr Bain would have to satisfy a Queen's Counsel his father was the murderer, Prof Kevin Dawkins said when contacted.
"It's extremely unlikely that any QC would conclude that he was innocent," he said.
That suggestion was slammed by Mr Bain's lawyer, Michael Reed QC, who responded: "All I can say is I live in the real world, not the academic world.
"We would not make the application if we did not think it was justified."
Justice Minister Simon Power announced yesterday he had received a letter from Mr Bain's lawyers formally notifying him of a claim for compensation for wrongful conviction and imprisonment.
Mr Reed said his legal team was "inviting dialogue with the minister" on a case he called "probably the worst miscarriage of justice in New Zealand history".
He did not know where Mr Bain was, but said he was "penniless".
Mr Bain was convicted in 1995 of murdering five members of his family in Dunedin. In 2007, the Privy Council quashed his convictions on the grounds of a substantial miscarriage of justice and ordered a retrial, and in June 2009 he was found not guilty.
Mr Bain's supporters refused to talk to the media last night.
Long-time advocate Joe Karam, asked what chance he thought Mr Bain had, said: "I don't have any comments to make."
The head of the Bain support group, Catherine Spencer, of Dunedin, said if Mr Karam would not speak about the matter, "I shouldn't talk to you, either".
After the retrial, Mr Bain's legal team began preparing the application for compensation.
About the same time, supporters of Robin Bain began an online petition to stop David Bain receiving compensation, and advertised in newspapers, calling for people to sign.
Prof Dawkins said Mr Bain would have to prove, on the balance of probability, he was innocent of the murders.
During his retrial, he only had to prove innocence beyond reasonable doubt.
"Because he maintained his father was the murderer, with a compensation claim, he would have to prove that Robin Bain was the murderer, to the standard of more likely than not, or the balance of probabilities."
On the question of compensation, he believed, if Mr Bain was to succeed, he "might expect a handsome payment".
Prof Dawkins noted Mr Bain's former cell-mate Rex Haig's case for compensation was refused by Robert Fisher QC because he could not prove his innocence on the balance of probabilities.
Mr Haig's conviction for the 1995 murder of fisherman Mark Roderique was quashed in 2006.
Arthur Allan Thomas, who was pardoned in 1979 for the murders of Jeanette and Harvey Crewe, was awarded $1 million.
David Dougherty, who was acquitted on DNA evidence in 1997 on charges of rape and abduction of an 11-year-old girl, was awarded $868,000 in 2001.
Based on Mr Dougherty's compensation, Prof Dawkins thought Mr Bain could receive between $2 million and $3 million.
"But, crucially, he has to pass the first hurdle."
Another possibility was that the Government could make an ex gratia payment "just out of generosity", but that was "most unlikely".
Colin Withnall QC, Mr Bain's lawyer from 1997-2004, said he was not sure the Cabinet guidelines for compensation went as far as Prof Dawkins was suggesting, but said he was not in a position to comment.
THE PROCESS
> The Justice Ministry initially assesses claims.
> Claims which merit further assessment are referred to a QC for advice.
> The QC reports to the Justice Minister on the merits of claims.
> If the QC is satisfied the applicant is innocent on the balance of probabilities, the QC will recommend an appropriate amount of compensation.
> Cabinet makes the final decision on the recommendation of the minister.
- Additional reporting Ellie Constantine, Allison Rudd and The New Zealand Herald.
