Australian Border Force agents in April found 1.6 tonnes of methylamphetamine and 37 kilograms (81.5 pounds) of heroin in vacuum-sealed packages hidden inside stereo speakers shipped from Thailand to Melbourne.
Police arrested two men and a woman in their late thirties on Wednesday following raids in suburban Melbourne, Australia's second-largest city.
Certain life-saving drugs in short supply
"Two of the three were customs agents. They are trusted insiders within the industry," Australian Federal Police deputy commissioner Neil Gaughan said.
He added they were not government employees but private contractors.
"They used their position of trust to circumvent the border controls that exist within Australia," he was quoted as saying by national broadcaster ABC.
Police said they were cooperating with authorities in Thailand where an investigation was ongoing.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ