"The brutality of ISIL terrifies everyone," the defector said during BBC's Panorama news show. "My family, my cousins, my siblings are all still there. I fear for them. If they can't reach me, they will reach my family."
He was nervous, agreeing to record an interview only after several hours of discussion. He would talk to us only if we would not reveal his identity. He wrapped himself in a keffiyeh for BBC camera.
He summed up the extremists' tactics: "If you're against me, then you'll be killed. If you're with me, you work with me. You submit to my will and obey me, under my power in all matters."
The defector had initially joined an extremist brigade of the so-called Free Syrian Army to fight the Syrian army. He joined ISIL when his entire tribe pledged allegiance to the group - and because he believed in creating a so-called Islamic state.
His first orders, as an ISIL militant, were to attend a course on Takfiri law. "Not the principles of Islam, the principles of the Islamic State. So they teach you the Islam they want," he said.
"It appeals to the heart and not to the mind, so that your heart becomes impassioned with their words. This is the first stage. The second stage is military exercises, military training."
He explained that ISIL had learned the lessons from Iraq in the early days on the anti-American insurgency. In Syria, the defector said, ISIL tried to do things differently as it entered each town.
"In the beginning ISIL used goodness with the population in order to attract the people and they provided them with what they needed in order to attract them quickly, because they suffered so much," he said.
"Once ISIL succeeded in attracting people they changed dramatically, from being good to being cruel and harsh. You're either with me or against me! There is nothing in between."
"Anything that contradicts their beliefs is forbidden. Anyone who follows what they reject is an apostate and must be killed," the defector said.
"The [so-called] Islamic State have brought in people from other countries, different nationalities who are quite young in age so that they can brainwash or indoctrinate them with their ISIL ideology," he said.
NTJ/MB