PARIS (AFP) - Khamzat Azimov, who kept his beard short over a youthful face, was not considered a major threat despite being on France's two watchlists for suspected extremists since 2016.
"It was his relatives who alerted the security services, as opposed to his behaviour, actions or ideas" which might have drawn scrutiny, a source close to the inquiry told AFP.
Yet on Saturday (May 12) night, the 20-year-old described by neighbours as a quiet student spread terror throughout a bustling area of restaurants and theatres just a short stroll from the historic Paris opera house.
Former classmates from his Strasbourg high school described Azimov as a religious and "very discreet" student who liked video games and sports.
The eastern French town where he grew up is home to a large community of refugees from Chechnya who fled the Muslim-dominated Russian republic during two bloody separatist wars against Moscow-backed forces.
One ex-pupil told AFP: "Khamzat was quite calm, he kept himself to himself, he didn't have a problem... He did Ramadan, he paid attention to girls."
The man who declined to be identified added that Azimov "had a distinctive manner and was in contact with Syria where he wanted to go. But after the bac (exams) he left all that, he wanted to make a living."
Another former pupil described a "normal student, not excellent but not bad either".
"We knew he was Muslim but he did not show it," the young woman added, saying he never talked about his birthplace Chechnya or the wars there.
Family fled Chechnya
Investigators have taken Azimov's parents into custody for questioning as well as a friend in Strasbourg.
The conflict in Chechnya gave birth to a fierce Islamic insurgency that would eventually produce fighters who would join other militant groups, including the Islamic State of Iraq and Syria, which claimed responsibility for Saturday's attack in Paris.
But a manager of the apartments in the northern 18th arrondissement of the French capital where the Azimovs rented a room said there was nothing overtly religious about the family.
Calling them "very discreet," the woman said "there was nothing ostentatious in terms of religion" and described Khamzat Azimov as a young man who favoured tracksuits and "said he was a student".
A neighbour also spoke of "a very discreet family, never any problems," adding that they "never received visitors".
And the son "wasn't a thug, but someone who was reserved," she added.
"They have been living here for a little over a year," said Reda, another resident in the building.
"The father worked sometimes, mostly in construction, painting. The mother worked for an association which helps the homeless," she said.
Witnesses to Saturday's attack said Azimov remained composed as he began attacking people with a 10-centimetre (four inches) blade shortly before 9pm (3am Singapore time).
"He approached calmly, a total contrast with the panic all around him," said Romain, 34, who was placing an order with his wife and six-year-old son at the Starbucks cafe on the Avenue de l'Opera.
"He had a beard, not very long, and was dressed normally. He didn't fit the stereotype" of a jihadist, he said.
Investigators have yet to reveal how Azimov became radicalised. One source told AFP he had been questioned by anti-terror investigators last year "because he knew a man who was in contact with a person who had gone to Syria." He did not have a criminal record, and became a French citizen as a teenager in 2010 following his mother's naturalisation.
But his attack echoed a similar one last October, when a knifeman who also carried no ID papers began stabbing people at the main train station in the southern city of Marseille, killing two people.
That attack was also claimed by ISIS.