A deal between US-backed Kurdish and Arab forces in Syria and ISIS sent thousands of fighters and families belonging to the terror group on a convoy out of harm’s way and deeper into the so-called caliphate where the fighters can regroup or smuggle themselves into other countries.

A group of truckers in Syria reportedly got called out to Raqqa, ISIS’s former Syrian capital, for what they thought would be a small job moving a few hundred people around. But it ended up as ISIS’s mass exodus from its former stronghold, according to a BBC investigation .

The US not only knew about the deal – they reportedly kept a close watch on the the convoy as it drove through the desert towards Iraq’s border.

Col. Ryan Dillon, spokesman for the US-led coalition fighting ISIS, explained to the BBC why the US knowingly accepted the deal.

“We didn’t want anyone to leave,” Dillon said. “But this goes to the heart of our strategy, ‘by, with and through’ local leaders on the ground. It comes down to Syrians – they are the ones fighting and dying, they get to make the decisions regarding operations.”