Speaking to a local TV channel ahead of the release of his autobiography in New Zealand, the former Kiwi skipper said he had no regrets about his decision to testify against his former teammate.
"Whether they believed me, whether they didn't. None of that really matters. It wasn't about a guilty or not guilty verdict. It was a matter of fulfilling a moral obligation I felt I had," he was quoted as saying in the New Zealand Herald.
Cairns was charged with perjury and perverting the course of justice after he successfully sued Lalit Modi for libel in the high court in 2012 after the former Indian cricket chief had sent a tweet in 2010 that implicated Cairns in match-fixing, which made him unfit to be included for the IPL.
During the libel case that resulted in a £1.4m settlement awarded to the former New Zealand all-rounder, Cairns, under oath, said he had "never ever cheated at cricket and nor would he ever contemplate doing so."
After nine weeks and evidence from some of the leading names in the cricket, the perjury trial of the former New Zealand all-rounder Chris Cairns ended with the 45-year-old being acquitted of all charges. McCullum was among the several cricketers who testified against Cairns during the trial in London last year.
"He was everyone's hero back then," said McCullum, "but it's dangerous when you meet your heroes, I guess".
McCullum claimed that Cairns approached him about match-fixing in 2008. Bazz was further quoted as saying, "I just simply didn't understand that if you weren't to report it, you were just as in the gun as anyone that has actually approached you. Once I realised that I straight away went and reported it."
"I didn't have to testify," he told Seven Sharp, a Television New Zealand program. "I think that's something that people don't understand. And I'm pretty sure lots of people wouldn't do what I did. But I felt I had an obligation, especially as captain of New Zealand, to go over and tell my side of the story."
Cairns was found not guilty of on all charges in 2015. When the media had asked him what was his response to McCullum's actions, he said that he didn't quite understand why he had done so. McCullum said, "The fact that the court case became about me versus Cairns is something I'll never understand."
"Under pressure, people show their true character. It's not the character I thought I knew, and I guess I can never forgive him for that. I'm sure he'll get on with his life, and I'll get on with mine, and let's hope they never cross paths," he was quoted as saying by the New Zealand Herald.
With his autobiography set to launch tomorrow, fans and the critics will be looking to get their hands on the book to know more about this issue.