An unpaid storage unit in Highlands Ranch has turned into the site of Colorado’s largest-ever fentanyl seizure.

Authorities say the unit—located in the south Denver suburb—went to auction after months of nonpayment. But when the winning bidder opened it, expecting maybe old furniture or forgotten belongings, he instead found nearly 1.7 million fentanyl pills.

Officials announced Monday it’s not only the biggest fentanyl seizure in Colorado history, but the sixth largest in the nation.

The discovery traces back to a Colorado Bureau of Investigation operation earlier this year. In April, CBI investigators wiretapped a drug trafficking organization tied to the Sinaloa cartel, one of the largest drug networks in the world. That investigation led to multiple arrests—including the man who rented the storage unit.

DEA Special Agent David Olesky says that arrest likely explains why the locker went unpaid and eventually up for auction. Olesky called the seizure “record-breaking” and said it represents countless lives saved. Authorities are not identifying the suspect because he’s currently facing criminal proceedings.

Inside the unit, investigators found 198 kilograms of fentanyl, equal to about 1.7 million pills, along with 12 kilograms of fentanyl powder and roughly two and a half pounds of methamphetamine.

Douglas County Sheriff Darren Weekly praised the auction buyer who reported the discovery, saying that person “undoubtedly saved countless lives.” Olesky added that fentanyl remains the leading cause of death nationwide for adults ages 18 to 45, and that just two milligrams can be fatal.

Officials say the seizure underscores the continued push by Mexican cartels to traffic fentanyl into Colorado—but also the determination of local and federal law enforcement to stop it before it hits the streets.