The Islamic State is also still sitting on the massive windfall that it built up during the height of its power. “What we know is that they accumulated large amounts of cash and other assets,” said Howard Shatz, a senior economist at the Rand Corporation and co-author of several studies on the Islamic State’s finances. “We don’t know where it all went.”

Some of those funds appear to have been invested in legitimate commercial enterprises. In October, a series of raids on Islamic State–linked businesses in the Iraqi city of Erbil uncovered a paper trail that suggested the group had invested in everything from real estate to automobile dealerships. These businesses are often run by middlemen who partner with the group not out of ideological sympathy but for profit, and then funnel revenue to the Islamic State when called upon.

The senior Iraqi security official told me that the bulk of the Islamic State’s assets had been transferred to Turkey, though the Treasury Department has sanctioned its money-services businesses in Syria and Iraq, which have connections as far away as the Caribbean. Some of these funds are reportedly held in cash by individuals in Turkey, while a portion has also been invested in gold. There is precedent for Ankara turning a blind eye toward the terrorist organization’s activity on its soil: The group used to make millions of dollars by selling smuggled oil to Turkish buyers. The October raid in Erbil also targeted the financial network built up by Fawaz Muhammad Jubayr al-Rawi, an Islamic State leader who the Treasury Department claims owned and operated Syria-based money-services businesses that exchanged money with Turkey. The Turkish government has consistently denied providing safe harbor to either Islamic State individuals or the group’s assets.