"It seems to me like the cocaine was probably part of a bigger lot, and this part has gotten away," said the retired detective.
"I would think they would be looking at shipping rather than planes - you'd be looking at boats coming into and out of the area.
"The most likely thing I would think is that a boat has come in and dropped it off and then someone else has gone out and picked it up."
He said the boats involved may have had their navigation or GPS devices turned off to avoid detection - but radar operated by the air force or other agencies may still have picked them up.
He suspected the drop-off boat would have had to get in "quite close" to Bethells due to its infamous rough waters. The pick-up boat would be smaller so ideally it wouldn't have to go out too far to sea.
"[Police] will be looking at the tide and weather patterns to work out when the drop-off might have happened," the retired detective said.
"They will be working out what direction it's likely to have come from, looking at internal intel to see if they can pick up on anything happening, and looking at the packages forensically.
"They will test the drugs themselves to see if there are any signatures as to where they might have come from, which country.
"And the packaging itself will tell them things - it will have multiple layers and they will be looking for anything forensic, that will be a starting point."
He said the drugs would "almost certainly" be imported by a gang.
"It seems to me like it's probably quite a reasonably sized operation, so losing a bit - because they probably have the same amount or more still that they managed to get through - means it's still worth it to them."
Cocaine usually came from Colombia or the Middle East, he said.
"Cocaine is pretty popular at the moment.
"There used to be a lot of manufacture in New Zealand but now we're getting much more importation."
The source said it was likely the cocaine had been on quite a journey to get to West Auckland.
"The police will be looking at shipping routes - Tonga has always been a waypoint for these operations," he said.
"You get it into the Pacific and then network it out to various places from there."
He said the operation sounded very much like a similar drug bust in 2016 when 500kg - half a billion dollars worth - of methamphetamine was found on 90 Mile Beach.
A source said the presence of shells on the netting in the Bethells Beach haul indicated the packages were out at sea for some time.
Police tested the packages and confirmed they contained cocaine.
"It is believed the amount found would have a street value of approximately $3 million dollars," said Detective Inspector Colin Parmenter.
"Police with the assistance of NZ Customs have conducted a thorough search of the beach and surrounding areas in an effort to locate any further packages.
"There is a small possibility that further packages may turn up on the beach and we ask any members of the public to contact us immediately if they do."
The police Eagle helicopter was out in the Bethells area yesterday conducting a search of the wider area.
Parmenter said regular patrols would be sent to Bethells in the next few days to check for further washed up items.
"Our inquiries are ongoing to identify where these drugs have come from."
A police source said it would take some time to work out who was behind the drugs.
Currently police had "no idea" where the cocaine came from.
Parmenter was calling on anyone with information about the drugs - or anyone who found anything further in the area - to contact police.
- Additional reporting Nicholas Jones
