Peter Foster says he's convinced Gold Coast man John Chardon murdered his wife Novy in 2013 and is as "guilty as sin".
The convicted conman appeared in the Brisbane Magistrates Court on Wednesday where he was the first person to give evidence in the businessman's committal hearing.
Foster claimed there was nothing in it for him when he started working with police in 2015 to try to extract information about Chardon regarding the disappearance of his wife.
The court heard he contacted investigators after a news broadcast about a search for Novy's body came on the television where the pair were both incarcerated.
Foster claimed after telling Chardon about the segment, the accused killer said 'well they won't find her there', before he proceeded to get his lunch and call his lawyer.
"He didn't seem at all perturbed," he said.
"If you didn't have anything to do with your wife's disappearance, you would just be sitting glued to the TV."
The court heard Foster then requested police provide him with a listening device for him to use when he was moved into Chardon's cell.
Chardon's barrister Tony Kimmins repeatedly asked Foster what he was after in return, be it a financial reward or a reduction in his sentence.
But the notorious conman held firm.
"At the time I just thought: 'Who's speaking for Novy?'," he said.
"I think if she was a blonde-haired, blue-eyed beach girl there would've been more of an outcry."
Foster claimed his involvement in the case was not supposed to be made public and he had been assaulted in jail as a result.
The court heard he regretted his decision to involve himself but since 2015 he had kept thinking of his idol, Brisbane Broncos rugby league coach Wayne Bennett.
"Coach Bennett would say 'you tell the truth and you do your civic duty'," he said.
Foster said his gut feeling was that Chardon was "as guilty as sin" for the murder of his wife.
Police charged him in June 2016, more than three years after her disappearance.
The 34-year-old Novy was last seen at their home on February 6, 2013.
Her car was found at a Nerang train station a few days later, but despite extensive searches and a $250,000 reward, her body has never been found.