ROME—For the last three years, police in the U.K., Italy, and Romania have been trying to figure out what three men convicted of stealing $3.2 million worth of “irreplaceable” books did with them.

This week, they got their break after searching a home in Neamt in northeastern Romania where they lifted floorboards to find a cement tomb with all 200 books carefully wrapped and hidden.

The spectacular book heist in January 2017 could be a Mission Impossible plot line, with two of the thieves cutting a hole in the skylights of a postal transit warehouse in West London, and then balancing on rafters and upper bookshelves while they fished original first edition tomes written by Galileo, Isaac Newton, and Goya off the shelves, skirting the laser detectors on the floors.

Police say the book thieves were part of a gang of 13 thieves who went on a rampage in 2017 and 2018, stealing electronics and other valuables from warehouses using the same skylight entry technique. Many of those thieves are still on trial with the last scheduled to wrap up in the spring of 2021.

The 200 books were being held in the high-security warehouse, ready to be shipped to a high-dollar book auction in Las Vegas. The books were owned by two Italian book dealers and a German company specializing in rare original literary works.

Surveillance tapes later showed that the whole operation took five hours and the men escaped around 2 a.m. with the books in duffel bags to a rented blue Megane station wagon parked down the road from the warehouse.

Romanians Daniel David and Victor Opariuc pleaded guilty and were convicted of the break-in and theft, while Narcis Popescu was convicted as an accessory for driving the getaway car. Four other Romanian nationals were convicted of various crimes connected to the heist, but no one ever said where the books were being hidden.

The thieves were found after a rental car agency reported a “strange cleaning fluid smell” in the Megane car. While the thieves did an admirable job cleaning up after themselves, they left a smudge of DNA on the headrest of the rental, which had been seen on the surveillance tape.

For three years, police searched 45 properties in the U.K., Romania, and Italy, hoping to find the books, which include Newton’s Principia.

Metropolitan Police Detective Inspector Andy Durham, announced the incredible find on Friday. “This recovery is a perfect end to this operation and is a demonstration of successful joint working between the Met and our European law enforcement partners in Romania and Italy—and at Europol and Eurojust,” he said. “These books are extremely valuable, but more importantly they are irreplaceable and are of great importance to international cultural heritage.”

The books will be returned to their Italian and German owners.