Gabriel nodded. Takfir was a concept developed by Islamists in Egypt in the nineteen seventies, a theological sleight of hand designed to give the terrorists a sacred license to kill almost anyone they pleased in order to achieve their goals of imposing sharia and restoring the Caliphate. Its primary target was other Muslims. A secular Muslim leader who did not rule by sharia could be killed under takfir for having turned away from Islam. So could a citizen of a secular Islamic state or a Muslim residing in a Western democracy. To the takfiri, democracy was a heresy, for it supplanted the laws of God with the laws of man; therefore, Muslim citizens of a democracy were apostates and could be put to the sword. It was the concept of takfir that gave Osama bin Laden the right to fly airplanes into buildings or blow up embassies in Africa, even if many of his victims were Muslims. It gave the Sunni terrorists of Iraq the right to kill anyone they wanted in order to prevent democracy from taking root in Baghdad. And it gave Muslim boys born in Britain the right to blow themselves up on London subways and buses, even if some of the people they were taking to Paradise with them happened to be other Muslims who wished to remain on earth a little longer.

“There is a leader of these young men,” Ibrahim resumed. “He has not been in Amsterdam long—eighteen months, maybe a bit more. He is an Egyptian. He works in an Internet shop and phone center in the Oud West, but he likes to think of himself as an Islamist theoretician and a journalist. He claims to be a writer for Islamist magazines and websites.”

“His name?”

“Samir al-Masri—at least that’s what he calls himself. He claims to have connections to the mujahideen in Iraq. He tells our boys it is their sacred duty to go there and kill the infidels who have defiled Muslim lands. He lectures them about takfir and jihad. At night they gather in his apartment and read Sayyid Qutb and Ibn Taymiyyah. They download videos from the Internet and watch infidels being beheaded. They have taken trips together. A few of them went to Egypt with him. There is talk about Samir in the al-Hijrah. There usually is talk in the mosque, but this is different. Samir al-Masri is a dangerous man. If he is not al-Qaeda, then he is a close relative.”

“Where does he live?”

“On the Hudsonstraat. Number thirty-seven. Apartment D.”

“Alone?”

Ibrahim tugged thoughtfully at his beard and nodded his head.

“You told Solomon about Samir?”

“Yes, many months ago.”

“So why follow me tonight?”

“Because two days ago Samir and four other young men from the al-Hijrah Mosque disappeared.”

Gabriel stopped walking and looked at the Egyptian. “Where did they go?”

“I’ve been asking around, but no one seems to know.”