The messages from Syria ping on Aghiad al-Kheder’s phone all through the day and night. Sometimes it can be overwhelming, but he knows he cannot afford to ignore a single one.
“Yes, no, no, I don’t recognise this one,” Mr Kheder said as he scrolled through the hundreds of photographs and voice memos on his WhatsApp messaging service from his home in Germany.
They all show men of fighting age at checkpoints in rebel-held areas of northern Syria.
Guards take pictures of every male arriving at these checkpoints and send them to a WhatsApp group with members across the world, in an attempt to catch Islamic State of Iraq and the Levant (Isil) fighters hiding among civilians.
The group is made up of more than 250 Turkish intelligence officials, Free Syrian Army officers and Syrian activists who lived under Isil, who work together to try to identify the jihadists.
They have just a few minutes to respond.
“His name is Mohammed Faiz al-Ahmad and he is from Deir Ezzor, but in the audio message he says he is from Hasakah and gives another name.
"He’s lying, I know who he is. He fought with Isil in Mikhan in the countryside of Deir Ezzor,” Mr Kheder told the Telegraph by phone. “You don’t forget a face.”
Some of the pictures are of men who arrested and tortured the group’s members, others are of those they had considered friends until they left to join the jihadists.
Mr Kheder is himself from Deir Ezzor, a city in the east of Syria which until recently was controlled by the extremists. He spent a year living under Isil until he managed to flee the country and claim asylum in Germany in 2015.
He now runs an anti-Isil activist group called Sound and Picture, which brings news to journalists from civilians inside the caliphate.
He said of the roughly 600-800 pictures he gets a day, some 10-15 are identified by the group as Isil fighters. The accused men are detained and taken for questioning, the rest are free to cross.
“They usually try to change their looks, shave their beards and their hair, but the group’s members still recognise them,” said Abu Abd al-Rahman, a commander in the rebel group Ahrar al-Sharqiya, which controls several of the checkpoints in the area.
Cmdr Rahman told the Telegraph his group saw an exodus of fighters five months ago, when Isil’s capital Raqqa was besieged by US-backed Syrian Democratic Forces (SDF). Since Raqqa fell in October, the numbers have soared.
He said Ahrar al-Sharqiyah is seeing up to 20 Isil fighters arriving each day at their checkpoints near the city of Manbij, many of them carrying fake Syrian ID cards provided by smugglers.
So far most of them have been Syrian or Arab.
“I ask those who reach us how they got here, they say the SDF let them go as they wanted them out,” says Cmdr Rahman. “The SDF hasn’t fixed the problem, they have transferred the problem to us.”
The question then is what to do with them all.
In the second part of the Telegraph's three-part series on leaving the caliphate, the paper explores what happens when fleeing Isil fighters get caught.
No way home
The Syrian opposition group holding British fighter Shabazz Suleman told the Telegraph the UK government was yet to make contact with them and has not made any formal extradition request to Turkey.
“We have tried for six weeks to contact the British, but it seems they are not very interested in having him back,” said Omar al-Abd, a member of the FSA battalion detaining Suleman on the Turkey-Syria border. “We will just have to look after him for now I guess.”
Suleman said he would only return to the UK if he could strike a deal to ensure a lenient sentence. Otherwise he would prefer to stay in Syria, where his hosts appear to be keeping him well-clothed and well-fed. “They respect me,” he told the Telegraph this week. “They treat me well.”
While some countries, including Qatar and Kuwait, have reportedly offered to pay to have their citizens returned, others refuse to take Isil suspects back.
Former Soviet states such as Ukraine, the Chechen republic, Turkmenistan and Uzbekistan, which suffer from their own Islamist problem at home, have turned down Turkey’s extradition requests.
While Europeans caught by Turkish border guards are arrested and their embassies contacted, jihadists from these countries are now simply being turned back to Syria.
But FSA-run prisons in the north of the country are already at capacity and expanding by the day, according to Bashir al-Haji, the area’s security chief.
In the five main prisons are some 500-600 detainees, in some cases 10 to a cell. They are processed by the courts in the city of Manbij and the town of Marea, but the huge backlog means many remain in jail for months before their cases are heard.
Up until the battle for Raqqa began in earnest in June, Mr Haji said every one of his foreign detainees offered money for their freedom. “Within 72 hours of a foreign fighters’ arrest we would hear from a Daesh representative, who would offer us money or an exchange with an FSA captive,” Mr Haji said.
He says one Saudi Arabian prisoner offered $100,000 for his release. “We thought he was kidding but his friend brought the money to us in cash, they said they had made it from oil deals they struck in Deir Ezzor,” said Mr Haji, who claims to have turned them down.
But he has not had a single such offer since the beginning of the so-called caliphate’s collapse.
“They are very dangerous men, who should not be released into the world,” he said. “Even the ones who have left Daesh are not defectors as such, they still hold the same ideology. They are like mercenaries, they only left the battle because they see it as their job is done.”
Women-only safe houses
Mr Haji said that while Isil’s men are arrested if caught, its female members are not usually detained.
As many as 220 foreign widowed or divorced Isil wives are currently in safe houses in north-west Syria, he said.
Some of the women are living in tents on Mr Haji’s land in Marea. In one camp there are seven women with 17 children between them, one from Germany, one from theUkraine and the others from Uzbekistan.
The 26-year-old German woman had married a Turkish man in 2009 after the two met in Berlin. But after Isil declared their caliphate he told her they were to move to Syria.
Like most of the women, her husband was killed in fighting. She tried and failed to reach Turkey and now has no more money to pay a smuggler.
“The women have been with me for nine months, I don’t know what to do with them,” Mr Haji told the Telegraph from a cafe in Gaziantep, southern Turkey. “I pay for their food and accommodation myself, but I cannot do this for much longer.
“But I have a responsibility,” he said, taking a drag of his cigarette. “There are a lot of people in Marea who would want revenge on Isil, so if they leave here then they will probably be killed.”
He also fears some of them may still harbour extremist beliefs. He has the guards at the safe house send him weekly “progress reports” on the women. “When we ask them questions about Daesh they tell us what they think we want to hear so it’s hard to tell,” he said.
“They say they are Muslim but we never see them praying, I think they just liked the idea of the caliphate.”
The women who do make it across the border to Turkey are much more likely than the men to make contact with their governments.
Foreign consulates in Ankara have been besieged by hundreds of women and children - the wives, mothers and offspring of jihadists - seeking permission to return home.
Domestic terror threat?
While few fought in battle many are evaluated to still hold Isil’s extreme ideology and are presenting a challenge to counterrorism officials from Western Europe to North Africa.
Turkey reported that it had deported a total of 4,957 foreign fighters caught crossing from Syria since 2013, 108 of whom British.
The UK says that of the estimated 800 Britons who left to join Isil, 400 have since returned.
Only 24 per cent of returnees have been prosecuted in the UK. Two high-level British Isil fighters have also been tried in Turkey, including Aine Davis, one of the so-called 'Beatles' who tortured and murdered Western hostages in Syria.
Officials in Ankara had been adamant that Davis would be prosecuted in Turkey rather than extradited to the UK, which expressed an interest after he was captured in 2015.
He received a seven-year sentence earlier this year.
According to the US government, 40,000 foreign fighters from 120 countries have travelled to Syria and Iraq since June 2014.
Based on data from the 79 countries which have released information, almost 7,000 foreign fighters have been killed on the battlefield and double that have escaped.
Official estimates suggest only a third foreign fighters who have departed Syria and Iraq are in prison. The rest have either returned home without entering into the criminal justice system or, in contravention of international law, have been deported to a third country and have disappeared.
Ankara has deported a number of foreign fighters to Malaysia, a choice destination because it is predominantly Muslim and offers visa-free entry to many of the countries which are refusing their nationals.
More than 30 Isil suspects were sent on planes to Kuala Lumpur, which has since lost track of them.
Experts warn that while the focus is on foreign fighter returnees, the real risk could be from Isil deportees who did not go home and are now unaccounted for.