On a crisp spring day in March, in the northern city of Sulaymaniyah, I met Abu Islam, a senior ISIS leader nicknamed the Ghost of ISIS by Iraqi intelligence for his elusiveness. He was escorted into a small office with faux-wood paneling and no windows at the Special Forces Security Compound in Kurdistan. His hands were manacled in front of him; he was blindfolded by a dark hood pulled over his loose black Shirley Temple curls. Long sought by the Iraqi government, Abu Islam was notorious for running clandestine cells of suicide bombers—some of whom were as young as twelve—and carrying out covert terrorist operations beyond the Islamic State’s borders. Having had a few years of religious training, he was also tasked with teaching the unique ISIS version of Islam to new fighters. Still in his mid-twenties, Abu Islam rose to become the ISIS “emir” of Iraq’s oil-rich province of Kirkuk.

Abu Islam’s capture, in October, was one of the most important in the campaign to defeat the Islamic State. Most of the ISIS élite have fled or been killed since Iraq launched its most ambitious military offensive, late last year, to retake Mosul. “He’s a guy we chased for more than two years,” Lahur Talabany, the head of Kurdistan’s Zanyari intelligence service, told me. “To pick him up and realize that we finally got him, it was a big catch for us.”

Over the past three years, I’ve covered ISIS from Iraq, Turkey, Lebanon, and at the Syrian border. In four decades covering the Middle East, I’ve interviewed the leaders of Hezbollah, Hamas, and the rank-and-file of many other militant groups. ISIS, which has kidnapped and beheaded journalists, has been the hardest rebel group to cover. In Sulaymaniyah, courtesy of the Kurdish intelligence service, I got access to Abu Islam and, separately, to a second ISIS fighter who admitted to committing a series of rapes and murders in the course of two years.

I sat at a desk across from Abu Islam, a nom de guerre, as he recounted his misadventures with chilling nonchalance. He initially gazed downward, refusing to look at me, an unveiled, non-Muslim female. His real name is Mazan Nazhan Ahmed al-Obeidi. Unlike most foreign fighters who joined the Islamic State, the majority of Iraq’s homegrown militants came from villages and farms, intelligence officials told me. Abu Islam was born in 1989 in the village of Rashad, southwest of Kirkuk. In June, 2014, after the ISIS army blitzed across the border from Syria into Iraq, he became one of its early recruits.

“I was a student in a Sharia college,” he told me. “I was following ISIS on YouTube, on Facebook, on Twitter. I loved what they were doing.” He was married, with a pregnant wife, when he left home to join ISIS. He did not see his wife, or his daughter, Aisha, until after he was captured. His captors allowed the family visit to soften him up for interrogation.

“Every man has a weak point,” a Special Forces officer, who asked not to be identified, told me. During the two-year manhunt, he had questioned members of Abu Islam’s extended family. “I personally have been to his house. I saw his wife when she was pregnant. I saw her when she gave birth. And I saw her when the child was a year old.”

In the ISIS underground, Abu Islam told me, he ran nine sleeper cells inside Kirkuk. “I was not important,” he insisted, more than once. Yet he admitted to staking out targets—vulnerable public sites, Iraqi military installations, and mosques where Muslims opposed to ISIS congregated— and plotting how and where to plant roadside explosives to kill soldiers and civilians. “And assassinations,” he said, almost as an afterthought, “that was part of the job as well.” As he described the choreography of a military jihad—which he compared to playing chess—he began to look me in the eye. He seemed emboldened by recounting the powers he once wielded.

I could not independently confirm much of what he told me in the interview, which took place in the presence of two Kurdish intelligence officials. The Iraqi media has written about him as a senior ISIS emir. One suicide bomber—a fifteen-year-old boy named Mahmoud Ahmed, who was later captured—described Abu Islam’s influence. The boy was dispatched, wearing a suicide belt hidden under a Barcelona soccer shirt, to bomb an Iraqi stadium last year. "When I reached the target … when I saw the young kids, I knew it was wrong immediately,” Ahmed told Britain’s Sky News, in December. He left the stadium and returned to his handler, who said, “ ‘Go straight back.’ I told him, ‘No,’ and he said, ‘This is an order from Abu Islam.’ ” The boy went back to the stadium, where he was intercepted by Iraqi security forces. His belt bomb was dismantled as he wept.

The Islamic State is on the verge of losing Mosul, where its forty-six-year-old chieftain, Abu Bakr al-Baghdadi, declared the ISIS caliphate, in 2014. Mosul is the largest city under ISIS control. Its loss would leave only small pockets of land under the group's control in Iraq, although it still holds chunks of Syria. I asked Abu Islam what he thinks today of Baghdadi, who is on the run.

“I do not agree with his policies now,” he said. “If he wanted to establish an Islamic State, he could have done it in a different way. His policy was wrong—the killing, the terrorizing, all these ways.”

Yet he had recognized Baghdadi as his leader until he was captured? I asked.

“Yes, he was my leader, my caliph,” he replied. “If I was still there, I would have stayed there."

“Maybe it is failing right now,” he added, “but the rise of the Islamic State is still going to happen, because it’s a must. God has said so in the Book. Sharia law, or the caliph, must rule on Earth. Maybe not in our time. Maybe in another hundred years.”

The fighters are still faithful, he said: “The young guys over there—no matter what, no matter if they lose everything—that mentality is not going to go away, even if the caliph gets killed. If these forces keep on taking their territory away and they don’t have a city or something like that, it’s going to be like it was before—underground. It’s going to be even more dangerous. The attacks are going to get even worse. They’re going to be against nations worldwide.”

Abu Islam’s core beliefs have not changed, either. Shiites are not real Muslims, he told me, and must all be slaughtered. (There are almost two hundred million Shiites worldwide.) Christians and Jews, he added, have three choices: convert to Islam, pay a tax, or be killed. “Even in the Bible,” he told me, “Jesus said that all people must convert to Islam. The prophet Abraham, before Jesus, said that as well.” Gays and lesbians, he said, should be “thrown from the highest building or they get burned.”