Things were different in Deir ez-Zor. The city was surrounded, and then, without any fighting, ISIS was gone. The same happened in Abu Kamal. There was some fighting, and still is, but some jihadists, including fighters from Europe, agreed to pull out, whereas no one knew where they were going.
Then, in late October, early November, ISIS suddenly surfaced in rebel-held territories in Northwestern Syria, Idlib, and Hama. These are the largest rebel territories home to more than two million people. Even other Islamists who fought ISIS in 2014 couldn’t believe it. They were sure ISIS had cleared out of the area.
There is 270 kilometers of regime-controlled territory patrolled by Russian planes and drones between Deir ez-Zor and where ISIS resurfaced. And suddenly, as if out of nowhere, you have tanks, trucks, and thousands of fighters. All opposition news agencies and US and UK sources showed ISIS was there, and that they came from territory held by the Assad regime.
A young Dutch ISIS fighter wrote to his family in September from Deir ez-Zor, saying how he would fight to the death if necessary. Another Dutch fighter wrote to the previous man’s family in early December, notifying them that he had died fighting in Hama province. We know he moved 270 kilometers. Many ISIS fighters do not communicate with the outside world, but Europeans talk to their families and the public. That is how we know for sure he took the journey.