It’s not just Western countries that have to pay close attention to citizens that go fight for ISIL and then return home. The problem is even more acute in Middle Eastern countries, which provide most of the foreign Moslems who join ISIL.
One example of how dangerous this connection is occurred in mid-March 2015 when Bahrain police inspected a bus that had travelled from Iraq via Kuwait and Saudi Arabia to Bahrain. The bus and passengers had been inspected twice in Kuwait and once in Saudi Arabia but when the Bahrain police did their usual thorough search they found a teenager carrying some electrical appliances which contained bomb making components (141 detonators, 41 electrical circuits, a remote control device and some cell phones). Kuwaiti police, who are usually very thorough, are investigating what happened so they can adjust their search procedures. Meanwhile the Bahraini police found that the teenager who was transporting the appliances was asked to deliver them to a Bahraini man who was a suspect in some terrorism cases. Bahrain has had problems with its Shia population that have led to violence and some bombings. Iran supports the Bahraini rebels but denies providing anything more than moral and diplomatic support.