Al-Hussain’s parents decided they had had enough. They closed their house in Mezze and fled to Lebanon with their two daughters, begging Mohammed to go with them. He refused, telling them he had to stay and fight for his country. As his family fled, al-Hussain began killing with a vengeance. He knew that the struggle was no longer just about removing President Assad. It was a full-blown war in which there could be only one victor.

Syria had been run by the president’s Shia Alawite sect, but the country’s Sunni majority had been the underdogs for a long time and wanted nothing less than complete control. Russia and Iran wanted President Assad to continue running the country, as did Lebanon. Together they poured billions of dollars into supporting the regime, while the US, the UK and France, along with Turkey, Saudi Arabia, Qatar and the rest of the Arab states, supported the Sunni-dominated opposition.

After the nerve gas attack, al-Hussain’s unit switched their allegiance to Islamic State, which had been formed from the rump of al-Qaeda’s operations in Iraq. Led by Abu Bakr al-Baghdadi, Islamic State had attracted thousands of foreign jihadists, lured by its promise to create an Islamic emirate from large chunks of Syria and Iraq. Islamic State grew quickly, funded in part by captured oilfields, taking first the provincial Syrian city of Raqqa and the Sunni city of Fallujah, in the western Iraqi province of Anbar.

As Islamic State grew, Mohammed al-Hussain was given ever more strategic targets. He was known as the sniper who never missed, and his notebook was filled with the names of high-ranking Syrian officers and politicians.

‘He’s coming out,’ said the Brit, but al-Hussain had already seen the front door open. The soldiers outside started moving, scanning the area for potential threats. Al-Hussain put his eye to the scope and began to control his breathing. Slow and even. There was ten feet between the door and the colonel’s SUV. A couple of seconds. More than enough time for an expert sniper like al-Hussain.

A figure appeared at the doorway and al-Hussain held his breath. His finger tightened on the trigger. It was important to squeeze, not pull. He saw a headscarf. The mother. He started breathing again, but slowly and tidally. She had her head against the colonel’s chest. He was hugging her. The door opened wider. She stepped back. He saw the green of the colonel’s uniform. He held his breath. Tightened his finger.