Najim Laachraoui was one of two men who blew themselves up at Brussels airport but those close to him have been left wondering how he could have been brainwashed so quickly.
The 24-year-old has been confirmed by the Belgian federal prosecutor as one of the suicide bombers who targeted Zaventem Airport on Tuesday with a bomb concealed in a suitcase.
That attack, combined with another explosion at a Brussels metro station, killed 31 people.
He has also been identified as the possible bombmaker for the Paris terror attacks, after his DNA was found on explosives used in the French capital during the November attacks.
His friends and family, however, remember a good student who was more interested in playing frisbee and football than murdering innocent people.
Laachraoui’s younger brother Mourad, 20, said he had been “a nice boy and especially intelligent” who enjoyed football and reading.
Mourad, a world-class taekwondo champion, said his brother had been a practising Muslim – like the other members of the family – but his radicalisation and involvement in the killings had shocked his family.
“I was moved and stunned.
“I didn’t want to believe it was him – but you can’t choose your family.”
He was remembered as a pupil with a perfect behaviour record at Sainte-Famille d’Helmet Institute in Brussels’ Schaerbeek district, the Catholic school where he finished his secondary education in 2009, before moving on to the Free University’s Polytechnic School.
A friend from his first year electro-mechanical engineering course there in 2012 wrote on Facebook: “I don’t understand how anyone can be brainwashed so quickly.
“How can you switch sides and blow yourself up when you used to play frisbee tournaments every weekend? I don’t get it.
“He was in my study group, we’d see each other every week, he came to my flat. It never felt like he’d shoot me.”
It is understood Laachraoui didn’t continue his study beyond the first year, with a friend saying he expressed a desire to switch to medicine.
But it later transpired that he had instead gone to Syria in February 2013.
His family had heard nothing from him since.
At the Catholic school, his headmistress Veronica Pellegrini said said she was at a loss to explain his change in behaviour.
She added: “He was a good student with an immaculate disciplinary record.
“He never had to repeat a year.”
Following his disappearance to Syria in 2013, he reappeared in September last year under the false name of Soufiane Kayal, when he was stopped on the Austria-Hungary border by police for a routine check.
Also in the car was Salah Abdeslam, the prime suspect in the Paris attacks who was arrested a week ago, and Mohamed Belkaid, killed on 15 March in a police raid.