Slow grind for foot and mouth probe

Police hunting the elusive foot and mouth hoaxer admit only a "big bang" breakthrough will lead to an arrest.

A May 9 letter which claimed foot and mouth disease had been spread in feed for livestock on Auckland's Waiheke Island sparked a multi-million-dollar biosecurity alert and fears of a trade backlash.

"In an investigation like this, it is the 'big bang' we need," said Detective Inspector Harry Quinn, who is heading the investigation.

"All of a sudden we will knock on the right door and speak to the right people."

Every suspect eliminated was progress towards finding the offender.

The hoax letter had a Manawatu Mail Centre stamp on it and there were claims at the time it may have been a Massey University capping prank, as it was posted the same day agricultural students graduated.

Authorities now believe a biosecurity exercise at the university may have inspired a copycat hoaxer.

- NZPA