A student said he warned his teacher about showing caricatures of the Prophet Muhammad, considered blasphemous by Muslims, days before he was decapitated on a Paris street in what French President Emmanuel Macron called an "Islamist terrorist attack".
Four relatives of the attacker, including a minor, were detained in the immediate hours after the attack in the middle-class suburb about 20 miles north-west of central Paris, police sources said.
"I am here as a teacher, as a mother, as a Frenchwoman and as a republican", said participant Virginie.
French anti-terrorism prosecutor Jean-Francois Ricard identified the victim as Samuel P.
Nine people have been detained in connection with the fatal knife attack targeting a teacher in northwest Paris, as investigators check whether the assailant acted alone or had accomplices, state-run France info radio reported on Saturday. He was later shot dead by the police.
Born in Moscow, the teenager had been granted a 10-year residency in France and was not known to intelligence services, Ricard said.
Ricard said Samuel had sustained multiple injuries and that an investigation for murder with a suspected terrorist motive, had been opened.
A woman stands next to flowers at the Bois d'Aulne college after the attack in the Paris suburb of Conflans St Honorine, France, October 17, 2020.
Mourners marched near the school in solidarity on Saturday, holding signs that read "I am a teacher".
The parents had complained about Paty's use of caricatures of the Prophet, which were shown in class as part of a discussion about freedom of expression.
Islam prohibits images of the prophet, proclaiming they lead to idolatry.
Police said they were investigating a tweet posted from an account that showed a picture of the teacher's head, and which has since been shut down.
"It is not a civilisation that kills an innocent person - it is barbarity", he told France Inter, adding that the litany of deadly attacks by Islamist militants or their sympathisers was devastating for France's Muslim community.
"He was murdered because he was teaching, because he was teaching students freedom of expression, freedom to believe and not to believe", said Mr Macron.
"I appeal for the unity of the adult world, to defend without fear and without reproach freedom, equality, fraternity and therefore secularism", he said. We hope that we have succeeded by giving you the full details and information.
Friday's terror attack came as Mr Macron's government works on a bill to address Islamic radicals, who authorities claim are creating a parallel society outside the values of the French Republic.
Chechnya is a predominantly Muslim Russian republic in the North Caucasus.
The teacher had discussed caricatures of Islam's Prophet Muhammad with his class, authorities said.
The magazine republished the cartoons in the run-up to the trial in September, and last month a young Pakistani man wounded two people with a meat cleaver outside its former offices.
Friday's attack was the second such incident since a trial started last month into the January 2015 massacre at the offices of Charlie Hebdo.