The United States handed over more than 400 ancient artifacts to Iraq on Wednesday, part of ongoing efforts to repatriate the country’s looted heritage. But this latest batch has a particularly intriguing back story — the antiquities were seized by U.S. Special Operations forces members as they raided the house of a leader of the Islamic State militant group.

The nighttime operation to capture the militant took place in eastern Syria in May, and the Delta Force troops did not come back with their prize. It was their first such ground mission in the country, and their main target, a man known as Abu Sayyaf who ran oil operations for the Islamic State in the area, was killed in an ensuing firefight.

But as the commandos scoured the compound for documents and laptops that could provide intelligence about the organization, they stumbled across artifacts thought to be dating back as far as 4,000 years.