Police in Spain said they arrested 12 people on Wednesday in connection to a cocaine-smuggling ring that mixed the drug with industrial plastic pellets in a bid to avoid detection.

Reuters, citing police, reported that the drug could not be detected during routine custom checks when used as an ingredient of the plastic pellets, which are used to make things like bottle tops. Once the shipments cleared customs, the cocaine was chemically extracted in three specially designed laboratories in the cities of Madrid and Toledo.

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One of the labs was reportedly capable of producing more than 1,000 pounds of cocaine a month. Police said the other two produced smaller volumes.

Authorities say the crime ring was run by a family of Colombian origin whose leader lives on the outskirts of Madrid.

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Police did not identify how much cocaine the gang was suspected of smuggling into the country but said they seized 66 pounds of cocaine paste, more than 1,300 pounds of pellets and large quantities of chemicals in what they described as Spain's biggest-ever seizure of cocaine-processing infrastructure.