Seven people – including two minors – are due to appear before an anti-terrorism judge as part of the investigation into the murder of French teacher Samuel Paty.
The 47-year-old was beheaded outside his school in a suburb of Paris after he had discussed images of the Prophet Mohammad with his pupils.
Investigators say the 18-year-old attacker, Abdullah Anzorov – who was shot dead by police – had been seeking to avenge his victim’s use of the images.
A parent, who had reportedly posted a video about the history teacher’s class, is included in the group of seven people along with two minors.
Prosecutors said the attacker had approached the two pupils outside the school and asked them to identify Mr Paty as he left school for the day.
It comes as French interior minister Gerald Darmanin said he asked local authorities to put mosques in the cities of Bordeaux and Beziers under police protection following threats.
French regional newspaper La Nouvelle Republique has also received threats on social media after it published a caricature of the Prophet Mohammad on its front page.
The paper published an earlier satirical drawing from magazine Charlie Hebdo to highlight the threat from Islamic extremists.
One of the paper’s journalists, Christophe Herigault, told BFMTV that while the vast majority had given the front page a positive reaction as a defence of freedom of speech, a small number had issued threats against the paper.
“There were four or five threats, notably on Facebook, which has led us to lodge a judicial complaint, as a matter of principle,” he said.
French President Emmanuel Macron has promised to intensify action against extremism in recent days.
France has said it will ban an Islamist group named after the late Sheikh Yassin as part of a crackdown on militants following the attack.
The banned group is named after a Palestinian Muslim leader and co-founder of the Hamas movement who was assassinated in 2004. Hamas has denied any links with the French group.
A national tribute in honour of Mr Paty is due to be held at the Sorbonne university in Paris on Wednesday.