There they found the dead man and nearby sighted the suspect armed with a knife-like weapon, who threatened them as they tried to arrest him.
The investigation is being directed by specialised anti-terrorism prosecutors.
The scene has been cordoned off and a bomb disposal unit dispatched because of the suspected presence of an explosives vest, the police source said.
Earlier today, police told members of the public to avoid the area.
He said the victim was murdered because he was a teacher and taught freedom of expression, after Macron visited the scene.
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Police officials told the Associated Press that the victim had received threats after opening a discussion "for a debate" about the caricatures about 10 days ago. The police spokesman said that information was being checked.
France's anti-terror prosecutor said it was investigating the attack, while Interior Minister Gerald Darmanin - who had been travelling to Morocco - confirmed he is returning urgently to Paris. Our unity and firmness are the only answers to the monstrosity of Islamist terrorism.
France has over the past several years seen a series of violent attacks carried out by religious extremists.
The paper recently republished the caricatures.
Weeks later, two people were stabbed outside the former Paris offices of Charlie Hebdo in an assault that authorities later said had been created to attack the newspaper's journalists a second time.
This is a breaking news story and will be updated as more details become available.