One of the attackers who blew himself up in Paris's Bataclan concert hall had missed at least three weekly check-ins with French police who were investigating him on suspicion of terrorism-related activity.
By the time an international arrest warrant went out in 2013, Samy Amimour was likely already in Syria. And by the time a trial date was set nearly two years later, he may have been well on his way to planning Friday's attacks.
SEE ALSO: Recovery just beginning for many of Paris wounded
As police investigate the attacks that killed 129 people, the revelation that at least one perpetrator slipped through the hands of authorities has exposed what some describe as flaws in France's procedures to track militant suspects, in particular the system of "judicial supervision".
The one-time bus driver, described by those who knew him as a quiet young man, vanished in September 2013 when he was under judicial supervision, telling his father he was headed to the south of France.
%shareLinks-quote="No doubt his shyness made him prey for those who wanted to brainwash him. He got radicalized, he quit his job, he closed up, cut himself off from his parents." type="quote" author="Jean-Christophe Lagarde" authordesc="" isquoteoftheday="false"%
A week later, even though his passport had been impounded, he was on the Turkey-Syria border.
According to an Italian police source, an international warrant for his arrest was not issued until October 20, 2013.
"Investigators will determine whether there was a failure," said Sebastien Pietrasanta, a Socialist lawmaker and specialist in anti-terror issues. "But a man who slips off the radar when it comes to terrorism matters, that is unacceptable."
Under the system, suspects in anti-terror cases who are deemed not dangerous enough or at risk of fleeing to be remanded into custody while under investigation are usually brought under police controls, in which they must give up their passports and come in for regular check-ins.
"Judges are always asking themselves" whether judicial supervision is adequate to keep track of suspects, Virginie Duval, head of France's main magistrates union, told Reuters.
"But we can't just put everybody in custody."
Suspects in the Paris attacks:
SHYNESS MADE HIM PREY?
Those who knew the 28-year-old in Drancy, the suburb northeast of Paris where he grew up, said Amimour's personality changed four years ago when he started attending a mosque in the nearby suburb of Blanc Mesnil, although the Muslim Cultural Association there has denied he was a regular worshipper.
"He was well brought up. He wasn't a delinquent," said Drancy's centrist mayor Jean-Christophe Lagarde, who knew the family long before the attacks.
"No doubt his shyness made him prey for those who wanted to brainwash him," Lagarde said. "He got radicalized, he quit his job, he closed up, cut himself off from his parents."
SEE ALSO: Stories of those who died in the Paris attacks
Born on Oct. 15, 1987, Amimour grew up with his parents and two sisters in a household that was not strictly religious in a five-floor apartment block, the back of which overlooks a mural of the iconic flag-waving Marianne, symbol of the French republic.
"He went to school with my daughters. He would play downstairs with the children.... He was kind, sociable, smiling," said an elderly neighbor, declining to be named.
"He just changed completely ... He stopped shaking women's hands, when he greeted my daughters he would no longer kiss them on the cheek," he said. The last time the neighbor saw him, Amimour had shaved his head and was wearing a traditional robe.
Like most of the area's youth, Amimour went to the local college, or secondary school, where he got good grades and did well in his final baccalaureate exam.
"He was calm, he did not want to draw any attention to himself," said a 20-year-old delivery driver who lives above Amimour's flat and gave his name only as Bertrand. "He should have gone on to do better things than us."
His only known employment was as a suburban bus driver, a job that public transport authorities said he left in October 2012 after 15 months.
It was not clear under what circumstances he left the job. What is known is that in the same month, Amimour was detained along with two other men from Drancy over suspicions they planned to go fight in Yemen.
The three were released, but an official case was opened and they were placed under judicial supervision.
THOSE TRUSTED VANISH
Such measures are not rare: there are now 95 people in France under judicial supervision suspected of wanting to join the ranks of militants in Iraq and Syria. Another 139, considered more dangerous or more likely to flee, are being held in custody, according to a judicial official.
Officials have acknowledged that they sometimes lose track of suspects freed under judicial supervision.
In May, Paris prosecutor Francois Molins told Reuters several people who had been "trusted" enough to be placed under judicial supervision had "disappeared".
For example, two men thought to be linked to a cell suspected of being behind a 2012 attack on a Paris Jewish deli have been missing for months after being freed under judicial supervision, legal sources said. The family of one told police they suspected he had gone to Syria.
A defense lawyer familiar with anti-terrorism cases said a decision to avoid custody in such cases would not have been taken lightly.
"It is a huge feat every time we get one," the lawyer, who declined to be named, said.
In the case of Amimour, judges ordered him to give up his passport and report weekly at Drancy police station while the case was being investigated, which he did for nearly a year, a judicial source said.
Two years after he stopped reporting to police, judges decided in August he and the two other men would be tried in absentia next January for criminal conspiracy in relation to terrorism over their planned Yemen trip, a judicial official told Reuters.
The trial of the other two, who are suspected to have fled to Syria, will go ahead.
Several magistrates told Reuters administrative procedures -- from noting absences to issuing a warrant -- would have taken time.
"Police stations are swamped," said Duval, the magistrate.
See memorials and reactions in the aftermath of the attacks:
DOING WHAT I LIKE
While Amimour was a fugitive, his father Azzedine, speaking under the pseudonym Mohamed, gave two interviews to Le Monde describing how his son told him in September 2013 he was heading for the south of France, only to call a week later from the Turkish-Syrian border.
"Don't be selfish, you wanted me to become a lawyer... Being here, I am doing what I like," his father quoted his son as saying in the first interview published in March 2014.
They spoke once a month via Skype, and the father even traveled to Syria last year to try to bring him back, he told Le Monde. When they met, his son, who called himself Abu Hajia, was on crutches and bore a distant smile.
"He was with another man who never left us alone. It was a very cold reunion," Azzedine said in the second interview published in December.
"He did not invite me back to his lodgings, say how he had been injured nor whether he had been fighting."
The father told Le Monde police did not question him about his trip to Syria when he returned.
"When Amimour was detained and his passport was seized, his mother was a little relieved as she thought he wouldn't be able to go anywhere," mayor Lagarde said. "But he still fled."
Lagarde said Amimour and the two other wanted Drancy men had become radicalized at the Blanc Mesnil mosque, one of three in the suburb. The mayor of Blanc Mesnil, Thierry Meignen, strongly denied that the mosque was radical in an interview with Reuters, however.
On a visit to the mosque, where the remains of a burnt-out car stood in a nearby car park, none of the lunchtime worshippers said they recognized the attacker.
"It's not the mosque that's radical," said one man who gave his name as Khaled. "But who's to know if there could be such people who come here."