Unfortunately, we won't be getting any answers to that any time soon, with the Ombudsman ruling that the information must remain secret:
The Chief Ombudsman is siding with the Government when it comes to disclosure of information around former Northland MP Mike Sabin.
[...]
Newstalk ZB has taken the issue to the Ombudsmen, but Chief Ombudsman Peter Boshier has ruled disclosure of details would prejudice maintenance of the law.
He's declined to give full reasons for his ruling, saying they would likely prejudice those interests as well.
We all know the reason for this; unfortunately no-one is allowed to say why. And the immediate application of s6(c), which protects important things like the right to a fair trial, is justified. But that's often a time-limited withholding ground, and information can be released once circumstances have changed. Unfortunately, the Ombudsman's decision isn't online, so we can't see if they stressed this and committed to future release should the circumstances permit. And, as the Ombudsman is immune to the OIA, we can't ask them for it either.
Sabin's resignation raises very real questions of accountability that the public deserves answers on. We can't get them now, for obvious reasons. But hopefully we'll be able to get them in the future, and hold the Prime Minister to account if he has displayed poor judgement.