McCullum spoke at a Dunedin luncheon yesterday, and while he could not say much about the match-fixing issue, he wanted to see it through for those who loved the sport.
''Obviously, there is a lot I can't say as there is a criminal investigation going on. But as a witness, I had to give evidence. I had to do that as a player,'' he said.
He said the ICC and the Metropolitan police were comfortable with the evidence he gave and the time it had taken.
McCullum (32) last spoke about the issue in May, following the leak of his evidence that he had been approached about fixing matches in both England and India in previous seasons.
He labelled those involved in match-fixing as selfish people who did not have the best interests of the sport in mind.
McCullum covered many topics yesterday during a question-and-answer session with Dunedin broadcaster Steve Davie.
Harking back to the weeks of turmoil when he inherited the national captaincy, he conceded the process of Ross Taylor losing the job was handled poorly.
''There would have been a far better way to handle the whole thing. It took Ross a long time to get over it. Ross is a very trusting person and his trust took a hit then. I do not know the perfect way to have done it.''
He said Taylor was an honourable person who would take on the captaincy when asked.
But McCullum said it had worked out for Taylor after being stripped of the role.
''In the last 12 months his game has developed immensely.''
McCullum praised coach Mike Hesson, saying he was tough and thought hard about the game.
''He is a little individual, I don't think he'll mind me saying that, but he has got a real steel about him and is a hard bugger.''
McCullum said the criticism levelled at Hesson when he started as New Zealand coach was ''despicable.''
He said the success of the team over the past year was not just due to the players but also the hard work of Hesson. It had been a similar model he had used in Otago and that was working on the national level.
The future of Jesse Ryder was up to the player himself, but McCullum felt if Ryder had not moved south to Otago last season then his career might already be over.
''I am one of his biggest fans and he has got so much talent, and he is going to have challenges for the rest of his life. But to me, the key is he has moved down here. He has people around him who see his faults and are prepared to stand by him and help him out. He has not had that before in his job.''
McCullum said his playing future was not looking too bad. His body was fine so long as he kept working on it. Giving up wicketkeeping had helped him and he was looking forward to the World Cup in the summer.
