"I'm just delighted for David."
"The tragedy is it has taken so long to get here, but in the end it was all worth it," said the Dunedin-based lawyer, who was part of Mr Bain's defence team for seven years following Mr Bain's first failed appeal.
Mr Withnall stepped aside in 2004, but remained involved in the background and last spoke to Mr Bain a week ago, he said.
"He is a remarkable person.
"It has been awful for him, sitting there and listening to everything - all the revelations about his family. I have seen the pain on his face at times."
Yesterday's verdicts did not surprise him, but he found it hard to find the right words to congratulate Mr Bain's supporter Joe Karam and the defence team.
"It has been such a huge job. I know from my own involvement in it what a commitment it is and was.
"Joe Karam, what can I say - 13 years of his life to do this. I have just got the utmost admiration for Joe and the whole team."
Mr Karam and Michael Reed QC both mentioned Mr Withnall outside the High Court at Christchurch immediately following the verdicts, to thank him and praise him as a "magnificent lawyer".
Mr Withnall joined Mr Bain's defence team in July 1996 when he agreed to a request from Mr Karam to review the file and see if there was any merit in Mr Karam's then claims of Mr Bain's innocence, following a failed Privy Counsel appeal.
"The more I went into it, the more evidence surfaced and the more compelling it became."
Mr Withnall was involved with the petition to the Governor-General, two references to the Court of Appeal in 2002 and 2003, and the 2003 hearing "that set the stage for the Privy Counsel to become involved".
The 2003 Court of Appeal decision left him doubting his objectivity and he stepped aside at that point "to get some fresh legs".
"I was just stunned at that decision. I couldn't understand how they came to the decision that they did."
