Former National MP Jami-Lee Ross told Police he could smell "political danger", prompting him to secretly record a phone call he had with then-party leader Simon Bridges.
The recording relates to a $100,000 donation from a Chinese businessman, which is now at the centre of a High Court trial.
The High Court trial relating to donations made to both the National and Labour parties back in 2017 and 2018 has entered its third week.
On Monday the court watched a recording of Jami-Lee Ross' formal police statement made a day after he held a press conference where he called Simon Bridges a corrupt politician.
The statement was made to a detective senior sergeant at Wellington Central Police. Ross claimed Bridges had filed unlawful electoral returns and provided a number of documents, messages and a recording as proof of his allegations.
Ross told the detective he made the recording as evidence in case it came back to bite.
"My thoughts were, this is a bit dodgy - potentially in breach of the law," Ross said in the interview.
"I felt uncomfortable by it so I thought to myself I needed some evidence if this comes back to bite the party in the backside.
"I knew that the money coming through the Botany account, that if shit hit the fan it would be all on me and I wanted to make sure that I had evidence that the party leader asked me to do this."
The judge-alone trial before Justice Ian Gault will continue tomorrow in the High Court.