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For 11 years, what kept Joe Karam fighting was visualising the moment David Bain walked free, his quiet dignity overwhelming the media throng.

At this point, Karam also imagined having a gold medal placed around his neck for his perseverance in finally having Bain's murder conviction overturned. Vindication, before all those who doubted him.

But instead of a victory lap, the six months since Bain's release have been the hardest for Joe Karam.

"It has taken a lot to recover from the euphoria of the Privy Council decision and David's release on bail and then have to get my feet back on the ground and prepare for another trial. Instead of a medal, it's like having a noose around my neck."

But Karam, despite long ago spending his considerable fortune on the case, has found the motivation to carry on.

While he'd rather be doing-up the modest farmhouse he bought with partner Lisa at Te Kauwhata, he's part of Bain's defence team, lending relatively new legal counsel his textbook knowledge of the 13-year-old cold case.

Instead of a retrial based on the evidence known at the time, Bain faces a new trial, with the Crown calling dozens of fresh witnesses and original witnesses whose stories have changed. "The police are throwing incredible resources at this. A whole new set of circumstances is being thrown at David so we have a whole new battle to fight."

Karam's been on the case since 1996, when he "very naively believed all I would do was take my concerns to the authorities who would take over from there. Unbelievably, they didn't - they thought I was the enemy."

The campaign went to the Court of Appeal twice, the Privy Council, and the Governor-General, before this year's "last throw of the dice" full Privy Council hearing. Along the way, Karam was sued for defamation in the High Court by two police officers for allegations made in David and Goliath, the first of his three books on the case. He took on the media, with litigation involving TVNZ, North and South magazine and the Herald.

"Stories were written which were not properly researched ... It started to feel like you're the only person who's seen a Martian walking down Queen St."

He blames New Zealand's small size for the closed shop justice system and a national characteristic to not rock the boat. "For many years the mainstream media, judiciary and politicians just thought of me as a raving redneck who'd lost the plot."

But Karam was never afraid to swim against the tide. He'd made the All Blacks fullback spot his own in the mid-1970s when he defected to professional rugby league in an era when being an All Black brought adulation, not money. By the early 90s, he'd made a fortune in various business ventures including hamburger bars and country pubs and the country's first major independent vending machine company. He had investment properties, a launch and racehorses and lived the high life on 10 acres at Clevedon, putting his children through private schools.

He gave all that up to prove Bain's innocence - living, he estimates, in 15-20 rental houses in the past decade. The former man about town with rich-list friends stopped socialising because people would inevitably buttonhole him about the case and he felt compelled to put them straight - "destroying the dinner party".

"So in the end you stop going out."

He would not have survived without the support of Lisa, his partner of seven years, and his three children - businessman Richard, barrister Matt and Simone, a farmer's wife and mother who lives nearby.

"It takes an incredible toll. When I started this my daughter was 13 and I was 44. Now I'm 55 and she's raising my first grandchild with another on the way and I'm still explaining [the case] to a new bunch of lawyers.

"Over time it became a little bit blurred as to why I was doing it. I wanted the fact that I was right to be proven. There was proving I wasn't the only one seeing Martians."

But mostly it's been about Karam's innate hatred of unfairness and urge to help those less fortunate - attributes he says he gets from his father.

"It's hard to say this without sounding arrogant but I know that I'm right. I don't think I could live with myself, knowing that I was right, if I had given up.