Police investigating the biosecurity threat letter say they're pleased with the response from the public with suggestions on who might be the author.

"Several calls from around New Zealand are being followed up but so far we have not yet found the person who wrote the letter," says Assistant Commissioner Peter Marshall.

The threat letter's envelope has a Manawatu postal centre date mark of 5pm, 9 May 2005.

"We're working our way through people nominated by members of the public and police as potential suspects. The public response has been very good but we'd welcome a lot more information."

He urges people to contact their local police station if they can help with suggestions on who is responsible for the letter. "We're also keen to hear from people if they saw suspicious activity around farms on Waiheke Island in the last week or so.

"You may be Island residents who noticed something odd or you may have been visiting Waiheke Island and seen something untoward.

"Please contact your local police if you can help."

In the meantime police have released a photo of the letter's envelope which has a Manawatu postal centre date mark of 5pm, 9 May 2005.

Assistant Commissioner Marshall says the letter's contents are still being analysed and forensically examined.

While we believe the letter is a hoax it's only prudent for us to investigate the matter fully. There may have been other activity by the author in support of the hoax which is why we're asking people to tell us if they have seen suspicious activity."

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