New Zealand police asked the public Monday to help with an investigation into an anonymous letter threatening to contaminate infant formula to protest the country’s use of a pesticide known as 1080. The letter, which contained milk powder laced with the poison, was sent to New Zealand’s national farming body and dairy giant Fonterra in November. The anonymous writer threatened to poison baby formula unless the government halted the controversial practice of using 1080 in pest control by March. The writer also warned of making the threat public if authorities did not meet the demand by the end of this month. Minister for Primary Industries Nathan Guy said officials conducted more than 40,000 tests on products since the threat and found no traces of 1080. Prime Minister John Key called it a “form of ecoterrorism” but said he was confident food products are safe.