Law enforcement officials said this week that they had taken down a “sophisticated” decade-long operation to ship drugs and cash through the United Parcel Service, leading to the arrests of 11 people and the seizure of commercial-grade equipment to manufacture illegal drugs.

The scheme involved transporting both large amounts of narcotics throughout the eastern part of the United States and cash back to the Tucson metropolitan area, United States Immigration and Customs Enforcement said in a statement on Tuesday.

Drug trafficking organizations used UPS employees, including drivers and supervisors, to avoid being caught by both internal systems at the company and by law enforcement agencies. But in 2017, officials from Homeland Security Investigations, an arm of ICE, and the Tucson Police Department found evidence that drug traffickers were using UPS systems and began investigating.

“This investigation has identified and mitigated vulnerabilities in the shipping infrastructure that has allowed for the undetected trafficking of narcotics for more than a decade,” said John Leavitt, commander of the Tucson Police Department’s Counter Narcotics Alliance.