As US intelligence analysts comb through electronic and paper documents seized from the lair of Abu Bakr al-Baghdadi, one question is foremost on their minds: How was the ISIS leader able to find refuge in a Syrian province secured by the Turkish military and its proxy forces? Three US national security officials told me that they want to know more about Turkey’s knowledge of Baghdadi’s whereabouts. One important task for the team now going through the material seized in the Baghdadi raid and another raid that killed organization’s spokesman, Abul Hassan al-Muhajir, is to map out the relationship between Turkey’s intelligence service and ISIS. Both men were hiding close to the Turkish border in Syrian territory. Muhajir was found in Jarabulus, a town in the Aleppo province patrolled by Turkish forces. Baghdadi was found in Idlib province, where there are numerous Turkish military checkpoints. It’s possible, of course, that two of the most wanted terrorists in the world managed to slip under the noses of a NATO ally. But US intelligence officials are suspicious. And this suspicion is based not just on where Muhajir and Baghdadi were found in Syria. In the beginning of the Syrian civil war, the Turkish intelligence service allowed foreign recruits from Europe and Africa to travel through Turkey into Syria. At the time, Turkey pursued a policy of regime change in Syria, supporting many extremist fighters against the government of Bashar al-Assad. More recently, the US government identified at least one senior ISIS official as based in Turkey. The US Treasury noted in August 2017 that the organization’s finance minister had relocated from Iraq to Turkey earlier that year. As one US official who works closely on Syria policy told me: “Turkey has done everything in its power to support the worst actors in the Syrian civil war.” Tom Joscelyn, a senior fellow at the Foundation for Defense of Democracies, told me the Turks have been known to raid al-Qaeda and ISIS safehouses and redoubts. More often, he said, US sources find cases of militants “roaming free,” raising the question of what Turkey’s real policy is on ISIS, just as in the first years of the Syrian civil war the CIA indirectly supported extremist elements fighting the Assad regime. Over time, US interests diverged from those of its ally, with the rise of al-Qaeda and the Taliban in Pakistan and ISIS in Turkey. Osama bin Laden was found in 2011 in Abbottabad, where Pakistan’s most prestigious military academy is located. Baghdadi was found in Idlib, an area of Syria under responsibility of the Turkish military. To this day, the US government has not accused Pakistan’s intelligence services of hiding bin Laden, though the US military considers elements of Pakistan’s military intelligence services to be working with the Taliban in Afghanistan. Trump has invited Turkish President Recep Tayyip Erdogan to the White House this month, although Erdogan said he may not accept the invitation after the House passed a resolution condemning Turkey for its role in the Armenian genocide. Meanwhile, the Turkish military has violated an earlier ceasefire in northern Syria and resumed its campaign against Kurdish civilians, according to Syrian Kurdish leaders. It was Kurdish-led Syrian Democratic Forces, remember, that cultivated the source that was able to find Baghdadi. US intelligence analysts may soon find out if the Turks knew where he was all along. Bloomberg