John Letts and Sally Lane told their son of their despair at his decision to travel to Isis territory

Messages from John Letts and Sally Lane show the emotional strain on the couple as they attempted to persuade their son to leave Isis-controlled Syria.

In often heated dialogue between the Oxford couple and Jack Letts, now 23, they pleaded with him, challenged his ideology and constantly professed their love for him even as they described their deep hurt and sense of betrayal.

Though not religious, the two supported Jack’s conversion to Islam at the age of 16. He had been diagnosed with obsessive compulsive disorder and Tourette’s and they believed Islam was just another one of his obsessions.

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But his grades crashed. He moved from the Cherwell School, a comprehensive, to a further education college. He was hardly ever home. He dressed differently.

His parents, who also have a younger son who is now 21, cooked Jack halal meals, bought him his first thobe and ferried him around mosques. When Jack said he wanted to go to Jordan to study Islam and the Qur’an, they bought his return flight tickets in May 2014, despite being told of fears by one of Jack’s friends that he may have been radicalised.

John Letts initially thought his son was on a “grand adventure”, the trial heard. Four months later, after a phone call from Jack informing them he was in Syria, followed by radio silence for several weeks, his parents’ lives fell apart.

“A father should never live to see his son buried,” Letts pleaded in September 2014. Another message read: ‘Jack, I’ve never begged you before but I am now. Please contact us. Your mother is collapsing with fear and sadness … You don’t have to die to help your fellow Muslims.”

The couple established he was in an Isis-controlled area, though they did not believe he was a fighter. “I’ve lost him,” Letts wrote to a family friend. “I feel terrified, betrayed by Jack, embarrassed, massively let down. I know he’s not a nasty boy. But he’s very stupid and I created him, with my armchair revolutionary shite.”

Letts told his son of his despair. “The light that filled our lives went out when you left, Jacko. Now we wait for a phone call and check Facebook constantly to see if you’re still alive.” The couple learned that Jack had married.

Some of the messages become acrimonious on both sides, as Jack berated his parents for their criticism of his ideology. “You hurt your mother and I very deeply, but I suppose we’re just nasty unbelieving western kafir enemies of Islam who need to be wiped out before your new utopian caliphate begins,” Letts wrote.

“I feel I’ve lost you and if I could forget I had a son called Jack this pain would stop. But I can’t and I never will. I will stand here beside your mother and suffer with her until the end.”

Lane, too, chastised Jack. “I’m sorry to say it, but I am very ashamed of you and the shame you have brought on us as a family,” she wrote in June 2015.

Jack hit back. “You lot brought me up without faith. You taught me and indoctrinated me to look down on religious people as brainwashed idiots [you know you did]. You taught me that life had no true purpose … that there’s no afterlife and therefore no final justice. You taught me disbelief and darkness. Why should I be grateful for that?” he wrote to his mother.

Lane replied: “We weren’t [aren’t] religious ourselves. But that doesn’t mean that we didn’t give you the ability to choose what belief you wanted.

“For my own sanity I have to believe you at least care about us a bit and if anything happened to us you wouldn’t just think ‘Good, that’s three less kafir in the world.”