Jeremy Kerr admits two blackmail charges over the November 2014 incident, where he sent letters to Fonterra and Federated Farmers threatening that if the Government didn't ban 1080 he would contaminate infant formula supplies with the poison.
While Kerr admits sending the letters, he disputes the Crown's case that he did it for financial gain. That evidence is being heard at a two-day High Court hearing in Auckland.
This morning police played Kerr's interview from last year to the court, where he admits sending the letters -- as well as one month later retracting the threats.
In July 2015 Kerr was visited by a detective as part of the investigation, and a month later the letter retracting the threat was sent to that same detective.
During the police interview Kerr originally denied sending the retraction letter, but after the detective interviewing him said they'd found information on a computer, Kerr admitted he had sent it.
"So you admit to writing the second letter?" the detective asked.
"Well I have no choice do I?" Kerr replied.
While he wouldn't admit to writing the original threat letters at first, he later did.
In the interview, police say DNA from the retraction letter was tested, and was said to be a likely match with Kerr.
Kerr appeared shocked by the revelation in his police interview, telling officers the finding was "staggering".
Kerr told the detective he "just cracked one day", and had no idea why he wrote the letters.
"I don't know why I did it, I honestly just snapped one day," he said.
Kerr said in the interview it had nothing to do with financial gain or his business involving Feratox - a rival pest control product to 1080.
Yesterday the court heard how Kerr earned royalties from each sale of Feratox, and the Crown's case is that he wanted 1080 off the market so sales of Feratox would increase.
Kerr said in the interview "I wasn't in a good state" when he wrote the letters.
"I was just really, really angry."
Kerr thought because he hadn't heard anything from police of media about the threats, nothing had come of it.
"I just assumed it had been ignored," he told police.
When asked why he wrote the letters, he said he didn't know.
"I can't describe what I was thinking at the time. I was extremely stressed."
At the end of the police interview Kerr was charged with two counts of blackmail, and said he was "sorry" for doing it.
The hearing has just been adjourned until 10th March and Kerr is due to be sentenced March 23.