A former farm employee is "pivotal" to their investigation into the theft of 500 cows from an Ashburton farm, police say.
Senior Sergeant Scott Banfield told Fairfax police inquiries centred around a staff member at Norvo farm "and his activities".
Banfield did not name the man.
In a statement police added their investigation had indicated "auditing systems and processes may have been open to abuse" and that they had spoken to several people about the theft.
They also warned farmers to ensure they completed background and reference checks before hiring.
Earlier this month nzfarmer.co.nz estimated Norvo owners would be out of pocket by around $2 million because of the theft.
Authorities urged anyone who may have information in relation to the case to come forward.
**Can you help? Call Ashburton Police on (03) 307 8424 or CrimeStoppers anonymous on 0800 555 111.