You have to keep in mind that there's a number of logistical hurdles that they have to jump through in Europe in order to get explosives or guns. So for example, the Villejuif shooter in April 2015 who planned to attack a church: According to French press reports, he was instructed by ISIS to go to a sandwich shop, and the weapons would be waiting for him in a car parked outside. He was just told the make of the car, told to go there, told to pick them up. Putting that kind of attack together, using encrypted communications or other means, is not easy.

I'm really curious as to the actual structure of the Emni [the intelligence unit that handles foreign attacks]. And Abu Muhammad al-Adnani, the head of it. There are so few pictures of him. We don't even really know what he looks like. For somebody with this outsized influence projecting murder abroad, you'd think that we would know a lot more by now. And then the role of the hostages.

It's become extremely difficult to speak to active ISIS members now. I was speaking to them in 2015, and the last one was killed in a drone strike.

One of ISIS' biggest propaganda coups was the beheadings of the aid workers and journalists. Is [Emni], the group that is exporting fighters overseas, also the one that was holding James Foley and John Cantlie and Kayla Mueller?

It seems to me that a 9/11-style attack is impractical.

We know that Muhammad waged war against the Qurayshi tribe, his own tribe, and it's from that conflict that much of the concept of jihad and verses that ISIS now uses to justify beheadings come from. A young man just told me that he went back and read this carefully [and saw] the prophet and his people were fighting the Quraysh because they were not allowing the prophet and his people to practice their religion.

People who have left the group talk about how a religious inspiration took them to ISIS. It was their feeling of being marginalized as Muslims in the society where they were living, and then buying into the promise of a caliphate and of a Muslim land that is governed as in the time of the prophet. I have yet to meet anybody, or speak to anybody, who was not religiously motivated at some level.