RMELAN — "The U.S.-led coalition'sairstrikes have weakened ISIS. We can no longer make any progress. Our oil fields and refineries have been hit."

Ahmad Derwish, 29, speaks calmly, his gaze fixed on me and the Arabic translator. The ISIS fighter had been brought into the Syrian police station's room blindfolded and handcuffed, wearing orange plastic sandals and sporting the long beard characteristic of Islamic extremists.

He says the terrorist group is clear about its plans. "As long as the coalition attacks our caliphate in Syria and Iraq, we'll carry out attacks in Europe."

Derwish was captured about a month ago during the offensive on al-Shaddadi, in the northeastern al-Hasakah region, an operation during which the Syrian Kurd, Arab and Turkmen soldiers that make the Syrian Democratic Forces gained control of the area. The coalition carried out 86 airstrikes during the fighting. More than 500 people were killed, among them 400 ISIS fighters.

Derwish's left hand is completely burned, his right arm is wrapped in gauze and his head shows wounds covered with dried blood. He was an emir, a commander in al-Shaddadi area, a strategic city located halfway between the two so-called capitals of the "Islamic State," Raqqa in Syria and Mosul in Iraq.

For the interview, Derwish was brought from a secret prison in northern Syria, where he usually spends his days in isolation. The soldier bringing him hides his face behind a mask, for fear of retaliation.

Wage cuts

ISIS is in crisis and has cut wages, he says. Until mid-2015, they used to pay their fighters $150 a month. But with falling oil sales, amid a global price drop, they've been forced to bring salaries down to $50. Similarly, the flow of foreign Islamic fighters who crossed into Syria via Turkey to join the terrorist group also has slowed down.

Before arriving in al-Shaddadi, Derwish was vice-emir in Sinjar, a city in northern Iraq where ISIS captured more than 2,000 Yazidi women before turning them into sex slaves. I ask him what would happen to me should I find myself on ISIS-controlled territory. "You'd have to convert to Islam, or you'd become a slave," he says. "If you were dressed the way you are now, without the niqab, you'd be whipped."

I'm a journalist and a Christian, I tell him. Would he find it acceptable to decapitate me, as was done with many other journalists? "No, because you could pay the jizya," the non-Muslim tax, he explains. "What's more, I don't behead anybody. My work in ISIS is to fight, I stay on the frontline and I kill with bullets, not by chopping people's heads off."

Derwish claims he didn't have any sex slaves because he was married. He did however "introduce" many soldiers to Yazidi women. According to him, a good-looking woman aged around 18 could be sold for $3,000. "Yazidis are infidels according to the Koran, so it's legitimate to use these women," he says.

What about the terror attacks in Brussels last month that killed 32, for which ISIS claimed responsibility? Were those legitimate too? "It's preferable that infidels die on the frontline. But it's always legitimate to kill those who don't follow sharia," or Islamic law, he says.

He claims he's killed 15 or 20 people, "more or less," and he feels no remorse. "I was defending my religion," he says.

Derwish was born in Homs, 100 miles north of Damascus. When he was young, he moved to Saudi Arabia with his father, a mechanic. That's where he was radicalized. Saudi Arabia is the cradle of Wahhabism, a fundamentalist branch of Sunni Islam that promotes a return to the "pure" religion of Islam's early days. Wahhabism establishes among other things that adulterous women should be stoned to death and that sex outside of marriage should be punished by decapitation (unless the woman is a sex slave).

Derwish studied pharmacology in Ukraine before returning to Saudi Arabia, where he worked as a mechanic like his father. When the protests against dictator Bashar al-Assad started in 2011, and war subsequently broke out, he decided to go back to his birth country. Assad is an Alawite, a follower of the Shia branch of Islam, which is marginalized in the Islamic world and condemned by Sunni fundamentalists.

Secret smoke

Several of Derwish's relatives were taken prisoner during the siege of Homs in 2012. His paternal uncle was killed by regime troops. Derwish first joined the Free Syrian Army, a militia initially formed of deserters from the Syrian army that received weapons from Saudi Arabia and Turkey, and support from the U.S. and EU.

He later joined ISIS and spent two years and nine months with the terrorist group, until his capture. "I thought that toppling Assad would solve all the problems, but I eventually understood that things weren't that simple, that there were many militias and a lot of people who wanted to be in charge," he says.

Almost 500,000 people have died since the war started in March 2011. Most of them died in fights against Assad's forces. More than 1.9 million were wounded. Life expectancy in Syria fell from 70 years in 2010 to 55.4 in 2015.

Derwish pauses and asks for a cigarette. But doesn't ISIS forbid smoking? Aren't offenders put in jail? "I smoke in secret," he says with a laugh.

He apologizes for not speaking English. He says he speaks Russian and asks if I understand the language.

"No, I'm from Brazil. Have you heard of it?"

"Yes! Rivaldo, Ronaldo, Roberto Carlos," he says, listing famous soccer players of the late 1990s and early 2000s. Derwish is a soccer fan, but he hasn't been able to attend many games lately. They were only allowed to watch the news, and even then, only broadcasts that didn't feature women as reporters or anchors.

He says he's never met or seen Abu Bakr al-Baghdadi, ISIS" leader, who's also a soccer fan. But for him there's no doubt he's alive. "And we obey him, we do what he orders, because he's the caliph."

Still, Derwish admits he's a little pessimistic about the prospects of the fight against infidels. "A lot of people used to be willing to sacrifice for the cause, to do everything for ISIS, but that's no longer the case," he says. "A lot a mistakes were made, the radicalization went too far and people are selling me and the group out."

The Kurdish People's Protection Units (YPG) militia, which is part of the Syrian Democratic Forces, claims that all prisoners will be judged, but they haven't determined yet what crime they'll be charged with. It's probable that the few ISIS militants who didn't die in combat will die in prison, one official says.

Derwish doesn't know what's in store for him. "I don't want to fight anymore. I no longer know what's true in this fight here in Syria. I have a lot of doubts," he says. He asks for help to lift up his shirt and shows us the two bullet wounds he suffered during the fighting.

"It's written in the Koran that we're all going to die," he says. "But Allah promised us heaven, because we killed the infidels."