In Syria, he became an “emir of war,” which The Wall Street Journal describes as “an unusually high rank for a fighter who hailed from Europe.” He reportedly helped train new ISIS fighters. A video discovered by Paris Match depicts Abaaoud dragging corpses in Syria. (It is, needless to say, painful to watch.) Later in 2014, he recruited his brother Younes, who was just 13, to come and join him. Younes Abaaoud was able to reach Syria without arousing suspicions. He has been described as the youngest European jihadist fighting with ISIS.

“I can’t take it anymore,” their father, Omar Abaaoud, told reporters earlier this year. He also joined a state prosecutor’s case against Abdelhamid. “He destroyed our families. I don’t ever want to see him again.” Omar has reportedly since returned to Morocco.

Abdelhamid Abaaoud later returned to Belgium—an exploit he described in an interview with Dabiq, ISIS’s slick English-language magazine. “Alhamdulillāh [thanks be to God], Allah chose me, Abuz-Zubayr al-Baljīkī (Khālid), and Abū Khālid al-Baljīkī (Sufyān) to travel to Europe in order to terrorize the crusaders waging war against the Muslims,” he said. “As you know, Belgium is a member of the crusader coalition attacking the Muslims of Iraq and Shām.”

Abaaoud was able to escape detection even though he was known to Belgian authorities as an ISIS fighter. He told Dabiq that an officer he encountered simply didn’t make the connection:

A brother had taken video footage of some of us before a battle, but his camera got lost and was later sold by a murtadd [apostate] to a Western journalist. I suddenly saw my picture all over the media, but alhamdulillāh, the kuffār [infidels] were blinded by Allah. I was even stopped by an officer who contemplated me so as to compare me to the picture, but he let me go, as he did not see the resemblance! This was nothing but a gift from Allah.

In Belgium, it seems, he quickly began making plans for terror plots. Counterterrorism officials believe he had ties to the perpetrators of a string of attacks in France and Belgium over the last two years, including an attempted shooting on a train over the summer foiled by three Americans. In January, Belgian commandos raided a safehouse he had helped establish, in what CNN called “the biggest firefight Belgian commandos have faced since World War II.” Two men whom he said he had traveled with from Syria were killed, but Abaaoud was not.

Officials announced that they had foiled a major terrorist plot, but Abaaoud slipped away, apparently returning to Syria, where he gave his interview to Dabiq. “All this proves that a Muslim should not fear the bloated image of the crusader intelligence,” he said. (The magazine is online, but be warned that it also contains horrific images.) This summer, Abaaoud was sentenced in absentia to a long prison term in Belgium for organizing terror. In October, the French military, which had recently expanded its operations to include air strikes against ISIS in Syria as well as Iraq, attacked a training camp for foreign fighters in Raqqa, Syria, reportedly in an attempt to kill Abaaoud. At first, the strike seemed to have worked; word got to his family that he had been killed. His sister Yasmina said, “We are praying that Abdelhamid really is dead.”