John Letts and Sally Lane, Parents of Jack Letts

Alongside the humanitarian fall-out from Turkey's invasion of northern Syria, there are grave security concerns. Not least, what will happen to the thousands of so-called Islamic State militants imprisoned by Syrian Kurdish forces? John Letts and Sally Lane are the parents of one such prisoner, British-born Jack Letts. He left the UK in 2014 to live in the so-called IS caliphate. Since then he's had his British citizenship revoked and his parents have been convicted under UK anti-terror laws for sending him money. What will become, and what should become, of Jack Letts?