All the newspapers have the story of how Helen Clark knifed the former Police Commissioner as their lead story.
It really is incredibly bad judgement to talk off the record to a newspaper, about your own Commissioner of Police, when he is the subject of a formal investigation. If the PM had evidence of wrong doing, then she should have been quoted on the record or released the official report, but to confirm off the record a rumour or allegation is just incredibly unprofessional and disloyal.
Clark would have known that the newspaper wanted confirmation so they could publish the allegation. And this was an untested alleagtion that had not been verified by either of the two parties involved. So by confirming the information, she knew it would undermine the Commissioner of Police, regardless of its truth.