Simon Bridges hopes to have an answer to who leaked his expenses by the end of the week.
"If not this week, certainly in the next fortnight," he told The AM Show on Monday.
"We'll know then, and we'll be as open and transparent as we possibly can."
Details of the National Party leader's spending were given to Newshub days before they were due to be released. Mr Bridges initially blamed the Government, but Speaker Trevor Mallard called off the parliamentary inquiry after receiving a text from the alleged leaker.
Mr Mallard said it was an internal matter for the National Party, which has been spending taxpayers' money on its own hunt.
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Mr Bridges says he has no idea who might be singled out as the leaker.
"I don't know. And the reality is I can't pre-judge on what happens. I haven't [been briefed] by the people involved."
In an opinion piece published by Stuff at the weekend, The AM Show host Duncan Garner said the investigation was an embarrassing own goal and the party was "tearing itself apart, limb by limb, fingernail by fingernail".
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But Mr Bridges says he has no regrets.
"These are things that actually... you've got to deal with. I think it's the right thing to do. But they don't affect my focus. That's why I'm not in the detail of all of this."
In his column, Garner said his sources tell him the investigation so far has found no one responsible.