A small hole could be the key to the mysterious cocaine haul discovered in a Fonterra shipping container.

A container carrying 952 bags of Fonterra milk powder was seized by police on arrival in Algeria last October.

In the container, police found 165 kilograms of cocaine with a New Zealand street value of more than $50 million.

Customs New Zealand documents released under the Official Information Act show the cocaine was stuffed in five handbags that were in the container with the milk.

An insurance inspection of the container in Algeria on November 27 found there was no sign that the door or locks had been tampered with.

However, inspectors found a small hole, measuring about 7 centimetres across, in the bottom of the container. The hole appeared to have been punched in from the outside but it was too small for a hand to squeeze through.

It was unclear whether it was big enough for a handbag to pass through.

Fonterra lawyer David Matthews said he would not speculate "on damage to containers outside of our control".

He also defended waiting seven days before informing Customs of the seizure.

"We . . . notified them of the incident as soon as it was appropriate - this notification was based on the anecdotal evidence we had at the time. Unfortunately we still do not have any hard facts."

Hard facts have been difficult to establish.

The Customs investigation was closed in December with few answers. The only details confirmed publicly are that the substance was cocaine and there was no evidence that Fonterra was involved in the smuggling.

Customs' debrief and final findings were released to The Dominion Post heavily redacted to protect "free and frank expression" of government officials.

What is known is that the milk powder travelled through the ports of Otago and Tauranga before heading overseas.

Both ports have assured Customs it would be impossible for drug smugglers to gain access to the container in New Zealand.

The container then passed through Cristobal in Panama and Valencia in Spain, before arriving in Algiers, Algeria.

Customs and Fonterra have had difficulty getting assurance about how the container was processed in ports in Spain and Panama.

Port weigh-ins could have helped pinpoint where the cocaine was added to the container.

- © Fairfax NZ News