A man who had left the terrorist jihadist group Islamic State, formerly the Islamic State of Iraq and al-Sham (ISIS), tells the BBC that the terrorist group uses young, brainwashed foreign men to impose a very specific, oppressive form of Sharia law– and kill anyone who stands in its way.

The man, who did not give his name and hid his face from BBC’s reporters for fear of himself or his family–still in Syria–being killed, explained the ISIS philosophy simply: “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.” 

Unlike many who join ISIS directly, this man says that he had previously joined an extremist wing of the Free Syrian Army to combat Bashar al-Assad and establish an Islamic state in Syria. His brigade then pledged allegiance to ISIS, incorporating him automatically into the terrorist group.

He says he found himself shocked when he was forced into ISIS training, and the version of Islam being imposed was too radical for him. The jihadist group teaches, he explains, “not the principles of Islam, the principles of the Islamic State. So they teach you the Islam they want… it appeals to the heart and not to the mind, so that your heart becomes impassioned with their words.”

The man also explained that he had seen ISIS use a familiar tactic in every new town they conquered: initially help the poor of that town and curry favor by helping build infrastructure, then establishing a brutal, murderous regime and wiping out anyone who dared defy their rule. 

“Once Isis succeeded in attracting people, they changed dramatically–from being good to being cruel and harsh,” he said. “You’re either with me or against me! There is nothing in between.” That appears to be the situation in Mosul, Iraq, one of the largest cities under ISIS rule. While reports began to surface that ISIS had begun winning over the people of that city by establishing stable electricity and water utilities, others have begun to report that ISIS is denying rations to Christians and Shiites, who are considered apostates.

The ease with which they can convince young men to commit vicious crimes against civilians, the defector explains, is largely due to the use of foreigners to commit these acts. “The 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 ISIS ideology,” he explained, “and so they control the areas, not through the local people but with their own forces and their own men, whom they prepare for this task.”

The man interviewed by the BBC is not the first ISIS defector, but one of a very few select men who have recanted their allegiance to the group. In February, CNN found another man who had defected from ISIS by convincing the group that he was dead. The man’s testimony is extremely similar to the BBC’s source. The group attempted, he explained, to use sharia law to impose total obedience to that group. Unlike the BBC source, CNN’s defector claimed to have allies still working within ISIS to take the group down from inside: