Several of the attackers are believed to have been French nationals who traveled to Syria to join ISIS. According to the French interior ministry, France is the largest source of European jihadis in Iraq and Syria with at least 570 French nationals fighting in the ranks of ISIS.
Abdalali Mamoun, an imam at a southern Paris mosque, was one of a 20-strong group who came to lay flowers near the Bataclan theater where scores of people attending a rock concert were gunned down. He urged young French Muslims to steer clear of ISIS's unholy war.
"You're mistaken," Mamoun said. "You're mistaken in supporting that movement, ISIS.
"It will drag you to your death, to hellfire, because suicide and slaughter are not permitted in Islam."
Another member of his group insisted that the killers were indiscriminate in their choice of targets. "As French citizens, and as human beings, we have been wounded by this attack," Yasser Laouti, spokesman for the Collective Against Islamophobia in France, said.
"They killed Christians, Muslims and Jews indiscriminately."
Sympathy for the dead does not, however, mean support for French air strikes against the ISIS stronghold of Raqqa, in Syria.
"I saw that yesterday, after what happened, (French President) Francois Hollande decided to bomb Raqqa," reflected human rights activist Samia Hathroubi. "Do we really think that bombing a city of 200,000 people will help us combat terrorism in our own country?"
French Muslims point to discrimination and poverty, political and economic marginalization as some of the reasons why so many young French Muslims have flocked to ISIS.
But Noura Mounira, a French woman of Tunisian extraction, instead blames home-grown extremists for targeting young people -- including her own nephew -- with a version of Islam that's alien to her. Her advice to him was simple: "Listen to your grandmother."
Two hundred meters away, municipal workers were washing away dried blood from the pavement outside the Bataclan as police lifted barriers that had kept people away. Removing the traces of radicalism in the French Muslim community will be far harder.