In what officials described Tuesday as a “sophisticated, well-planned” heist, thieves scaled the walls of an Eli Lilly warehouse, cut a hole in the roof, slid down ropes and loaded dozens of pallets holding $75 million worth of prescription drugs onto at least one truck.

The thieves also disabled the alarm system at the 70,000-square-foot warehouse, one of three distribution centers in the nation for the international pharmaceutical firm. The robbery took place sometime early Sunday but was not discovered until later in the day, when an employee showed up for work, authorities said.

“It certainly has the appearance of a sophisticated, well-planned criminal action,” said Edward Sagebiel, a spokesman for Eli Lilly & Co. “We are conducting a full investigation and working with authorities . . . with the intention of recovering the products.”

Enfield Police Chief Carl Sferrazza described the heist as “extremely substantial” and said enough drugs were taken to fill at least one tractor trailer. “I can tell you it was many, many pallets,” he said. “They might have spent at least a couple of hours unloading all these drugs.”

Sferrazza expected the FBI and the Drug Enforcement Administration to join the investigation. “This will turn out to be, unfortunately, the largest theft that our town has ever experienced,” he said.

Sagebiel said drugs including Prozac, Cymbalta and Zyprexa were stored at the facility, but he said he could not say which drugs were taken.

No arrests have been made.

cdempsey@courant.com

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