A group of United Parcel Service (UPS) employees allegedly helped import and traffic massive amounts of drugs and counterfeit vaping oils from Mexico during the past decade, as part of a scheme that exploited a vulnerability in the company's distribution system, according to police.

The lucrative operation at times involved moving thousands of pounds of cannabis and narcotics each week from drug traffickers into the United States to destinations across the country, using standard cardboard boxes that were carefully routed through the private carrier's trucking and delivery systems, authorities said.

The cash the operation generated was used to buy opulent homes, vacations, properties and luxury vehicles, detectives said.

Four UPS employees have been charged with drug trafficking in state court, and court records show that at least 11 people – including two UPS supervisors and drivers – have been arrested in the past two weeks on a slew of state charges stemming from the decade-long investigation by a task force of local, state and federal law enforcement.

Investigators from the Counter Narcotics Alliance said accused ringleader Mario Barcelo – a UPS employee for 20-years – used a simple method to obscure the origin and destination of drug shipments, a tactic they worry could be replicated by other UPS employees and other drug-trafficking organisations.

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Authorities said Mr Barcelo used his position as a supervisor in the Tucson distribution facility to ensure known drug shipments were loaded onto the correct trucks and were delivered on time to their destinations without any interference or drug interdiction, bypassing security measures the employees knew well.

Attempts to reach Mr Barcelo were unsuccessful, and it is unclear whether he has a lawyer, as none was listed on publicly available court records in the case.

Tucson-area law enforcement had been tracking Mr Barcelo since at least 2009, but Sergeant William Kaderly said detectives were frustrated for years that the company did not work more “proactively” with them to intercept and prevent the suspected criminal behaviour.

Mr Barcelo was arrested on 13 November.

“He's been able to provide this service to drug traffickers without being detected both internally and externally by law enforcement for years,” said Mr Kaderly. “They've been doing it for so long that they were truly comfortable that they were never going to get caught.”

UPS said in a statement that the company is cooperating with law enforcement officials but that the company is “not at liberty to discuss the details of the arrests as this is an ongoing investigation”.

The Arizona attorney general's office, which is prosecuting the case, declined to comment. Some of the defendants were arraigned this week, but prosecutors have withheld specific details of the investigation from public court record because more arrests are expected soon.

Some of the indictments have been sealed, police said.

Mr Barcelo and his alleged associates expanded the operation over time, transitioning from delivering cannabis to dealing in more valuable drugs and vaping pens.

Mr Barcelo used money made from the operation to fund a lavish lifestyle (Tucson Police Department)

Similar black market vaping pens and oils have been linked to the deadly outbreak of lung disease that has sickened nearly 2,300 people and killed 47 nationwide.

The drug-ring operators, who allegedly learned how to bypass all security systems, were shipping several thousand pounds of drugs a week at the peak of operation, increasing profits the farther east the packages were delivered, Mr Kaderly said.

“Their sales pitch was that because of who Mr Barcelo was at UPS, he could make sure your package will make it out without anyone finding it,” he said. “He had face time with traffickers.”

In one instance in 2017, investigators said they learned of a shipment but were prevented from entering a UPS distribution facility to investigate and intercept it. UPS spokesman Matthew O'Connor declined to provide details about the case, referring questions back to “law enforcement personnel”.

The company also declined to answer questions about the suspected “vulnerability,” as police described it, in its internal delivery system that the alleged conspirators used to carry out their enterprise.

Charging documents obtained by The Washington Post show that progress in the case did not come until 2017, when detectives identified some of the UPS drivers who were allegedly involved in the scheme and got investigators inside UPS's fraud and security divisions to help.

Undercover officers posing as drug traffickers contacted Mr Barcelo's associates to ship parcels containing sham cocaine and cash over several months in 2018 and 2019.

Investigators also placed GPS trackers inside the boxes, documenting the packages' movement from the homes of the individuals charged in the conspiracy to the UPS hub and out for delivery.

Police also tapped the phones of UPS employees and collected video footage of the group as they coordinated using the WhatsApp messaging app for the loading, handling, shipping and retrieval of cash and boxes from undercover agents, authorities said.

Along with Mr Barcelo, UPS supervisor Gary Love, and drivers Michael Castro and Thomas Mendoza face charges of money laundering, drug possession and drug distribution. Seven others are facing charges related to the shipping of the drugs and operating stash houses for the illicit materials.

One defendant, a 26-year-old, is suspected of being a member of a larger drug-trafficking organisation in Mexico; he and an associate charged undercover agents $2,000 (£1500) to accept a fake drug shipment and deliver it into the US.

Surveillance of Mr Barcelo, including wiretapping and undercover work, led police to Raul Garcia Cordova who was arrested 21 November on more than a dozen charges. Police raided his mansion and seized a boat, a Chevrolet Corvette, and a Range Rover. Investigators found 50,000 counterfeit vaping pens in a storage locker, officials said.

Local television stations captured footage of the Swat operations at Garcia Cordova's home last week as police hauled away the vehicles along with ledgers, cash and cannabis found hidden under a hot tub. Police say the man financed the operation.

“It was purely greed-driven,” Mr Kaderly said. The UPS employees “make nearly six figures with benefits, but at some point, greed just took over.”