Relatives of Aurélie Châtelain outside the city hall in Caudry, France, her hometown, before a march on Sunday. Credit Francois Lo Presti/Agence France-Presse — Getty Images
PARIS — When news reached her hometown in northeastern France that Aurélie Châtelain, a 32-year-old fitness instructor and mother of a 5-year-old daughter, had been shot and killed in a Paris suburb, few who knew her could fathom why.
But after the French authorities announced last week that the suspect in Ms. Châtelain’s killing had been arrested in connection with planned attacks on at least one church, it seemed increasingly apparent that her death was a tragic twist of fate, when being in the wrong place at the wrong time apparently put her in the path of a would-be terrorist.
That man, a 24-year-old student identified by the authorities as Sid Ahmed Ghlam, has been detained.
In a city still jittery from a terrorist rampage by three jihadists in January, investigators are scrambling to piece together what his plans were, whether he had accomplices and how he was involved in Ms. Châtelain’s death.
On Monday, the Paris prosecutor, François Molins, told France Info Radio that three men had been arrested over the weekend in connection with the investigation. While Mr. Molins did not detail whether the men were involved in the plot, he said that Mr. Ghlam had “acted following instructions given to him, in all likelihood, from Syria, on behalf of terrorist organizations,” though it was not clear whether he had ever traveled there.
Last week, Bernard Cazeneuve, the interior minister, said it was possible that Mr. Ghlam was on his way to carry out a massacre at a church outside Paris when he crossed paths with Ms. Châtelain and tried to steal her car to use it to hide his tracks. Mr. Ghlam was arrested hours later after he called an ambulance for treatment of a gunshot wound to the leg.
Police found an arsenal of heavy weapons, including several AK-47s, handguns and bulletproof vests, in his car and at his apartment in the 13th Arrondissement in southeast Paris. They also found a trail of online exchanges with people abroad that seemed to indicate he was being coached to carry out an attack on a church.
Mr. Ghlam has been placed under formal investigation on eight charges, including homicide, weapons possession, theft and criminal association, with the intent to commit a terrorist act. Mr. Ghlam’s lawyers have said their client denies all the accusations.
Many details about Mr. Ghlam, who is Algerian, and his plans remain sketchy, but information provided by the authorities and reported in the French media paint the picture of a young man whose radicalization went unnoticed by those close to him.
That he had been flagged by French intelligence services as a security risk and had come on their radar twice raised troubling questions about their ability to monitor a vast proliferation of potential terrorist threats at home.
Mr. Ghlam’s background seemed to point to another potential danger, of jihadist sympathizers who could be radicalized for terrorist acts over the Internet without ever leaving their countries of residence, far from the battlefields of Syria or Iraq.
Mr. Cazeneuve, the interior minister, said intelligence services had first summoned Mr. Ghlam in the spring of 2014 — after he expressed a desire on Facebook to go to Syria, according to reports in the French media — but found nothing suspicious. A second round of checks was just as inconclusive early this year, after Mr. Ghlam returned to France from a trip to Turkey.
Éric Denécé, director of the French Center for Research on Intelligence, insisted that “there were no flaws in intelligence gathering, because you cannot keep every single person under surveillance all the time — we don’t have the means to do so.”
“This attack was thwarted by accident,” he said. “But intelligence gathering is not an exact science, and chance plays a role.”
Unlike Chérif Kouachi and Amedy Coulibaly, two of the three Islamist extremists who killed 17 people in and around Paris in January, Mr. Ghlam had no past convictions and disconcertingly little in his background to indicate he would contemplate a terrorist act.
“Coulibaly and the Kouachi brothers had either been through organized crime or through foreign networks,” Mr. Denécé noted. “At this stage, I can’t think of other terrorists who were radicalized solely on the Internet without having been abroad.”
Mr. Molins, the prosecutor, described Mr. Ghlam as a single, childless Algerian citizen who came to France with his mother in 2001 to join his father, who was then living in St.-Dizier, about 130 miles east of Paris. He went back to Algeria in 2003, finished high school and returned to France to study computer science.
In September 2014, Mr. Ghlam enrolled at Pierre and Marie Curie University in Paris to enter the third year of a bachelor’s program focused on electronics. According to a university statement, Mr. Ghlam stopped going to classes in October.
In December, the statement said, he did not go to final exams, and came under disciplinary action because of suspicions he had falsified the grades on his academic record when he enrolled.
But Mr. Ghlam, who lived in a small apartment in a student-housing complex, did little else to attract attention and showed no clear signs of radicalization.
“We had never had anything to report on this student until the recent events,” said Constance Blanchard, a spokeswoman for the Crous, an organization that provides university students with housing and financial aid.
Hind Ghlam, Mr. Ghlam’s sister, told the newspaper Le Parisien that her brother had not presented any outward signs of being a radical Muslim.
“Sid Ahmed doesn’t have a beard, he doesn’t wear the djellaba, he prays five times a day, that’s it,” she said, adding that her brother gave Arabic language classes at a local mosque.
Ms. Ghlam told the BFM TV news channel that her brother had expressed no sympathy for terrorist groups abroad such as the Islamic State. “He would tell us: That isn’t Islam; Islam isn’t fighting with blood, it isn’t killing people,” she said.
Anonymous police officials told Agence France-Presse that Mr. Ghlam seemed to have been “remote controlled” by one or more individuals abroad, possibly in Syria, who had ordered him to target churches and told him where and how to get weapons.
The planning could not account for a carjacking gone wrong. DNA and ballistics evidence from Ms. Châtelain’s car, where she was found dead April 19, clearly implicated Mr. Ghlam, according to Mr. Molins.
Ms. Châtelain was in the southern Parisian suburb of Villejuif for a one-week training program that would have enabled her to teach Pilates back home.
“It really is bad luck,” said Guy Bricout, the mayor of Caudry, her hometown, who knew Ms. Châtelain from her time as a town councilor from 2008 to 2014. “She gets into this training program, she goes to Villejuif, and she crosses paths with an assassin.”
Many in Caudry feel that Ms. Châtelain played a role in avoiding a potential massacre. Mr. Bricout said he was going to ask that Ms. Châtelain be decorated posthumously with the Legion of Honor, France’s highest decoration. He said he would not be surprised to learn that Ms. Châtelain had put up a fight.
“By her resistance and courage, she helped avoid a much greater tragedy,” he said.