Ayoub El Khazzani, a 26-year-old Muslim, was known to Spanish and French police for his drug-dealing convictions and his frequent attendance at a radical mosque. A Morrocan, he had a Spanish residency card allowing him to travel freely throughout the European Union. He was on watch lists, but the lists contain far more names than police can track.

The ideology of ISIL creates people like Khazzani. Equipped with ISIL belief systems, a murderer can kill in good conscience because he thinks he’s fulfilling the wishes of God. A sense of divine justice provides moral strength, even when victims are fellow Muslims.

ISIL can acquire murderous followers without meeting them or knowing their names. The chief of ISIL and the caliphate, Abu Bakr al Baghdadi, may well hear of atrocities committed in his name and wonder at the identity of the perpetrators. It may be that psychopaths adopt ISIL beliefs to justify their own murderous instincts.

We are baffled by a form of evil that believes in its moral superiority and proudly advertises its crimes by video.