President Francois Hollande has unveiled plaques to the victims of last January's jihadist attacks in Paris as anniversary commemorations begin.
Seventeen people died in three days of attacks targeting Charlie Hebdo magazine, police and a kosher store.
The widow of a murdered policeman is taking legal action over alleged failings by the security services.
Ingrid Brinsolaro said threats against Charlie Hebdo had not been taken seriously enough.
The first plaque was unveiled on Tuesday outside the former offices of Charlie Hebdo, where 12 people were shot dead.
However it was immediately covered up as onlookers expressed shock that the name of one of the victims, Georges Wolinski, had been spelt incorrectly with a Y.
Mr Hollande then took part in further ceremonies for a policeman killed as he chased the Charlie Hebdo attackers, and at the Jewish supermarket in eastern Paris where four shoppers died.
Paris, January 2015: Three attacks in three days
- Wednesday 7 January 10:30 - Kouachi brothers storm Charlie Hebdo offices, killing 11 people. They then murder a police officer nearby
- Thursday 8 January 08:45 - Amedy Coulibaly shoots dead a policewoman and injures a man in the south of Paris
- Friday 9 January 12:15 - Coulibaly takes hostages at a kosher supermarket in eastern Paris. Four people are murdered
After the January 2015 attacks, the supermarket killer Amedy Coulibaly was also linked to the shooting and wounding of a 32-year-old jogger in a park.
However, the jogger has told BFMTV that he saw the gunman and he was convinced it was not Coulibaly.
The widow of Franck Brinsolaro, the police bodyguard employed to protect Charlie Hebdo editor Stephane Charbonnier (Charb), said there had been a "flagrant lack of security" around him even though threats had been made.
Speaking to RTL (in French), Ingrid Brinsolaro said her husband had complained that there had not been enough resources invested, that it was impossible for him to do his job properly.
Earlier, her lawyer, Philippe Stepniewski, filed a legal complaint with the Paris prosecutor's office, saying Mr Brinsolaro's death was "involuntary homicide".
Ms Brinsolaro told L'Eveil Normande newspaper that she felt forced to take legal action after the security services repeatedly failed to explain why her husband "did not have the means to do his job".
Interior Minister Bernard Cazeneuve has defended the government's efforts to ensure security.
Amid the commemorations, Charlie Hebdo has sparked anger with the cover of its special anniversary edition due out on Wednesday.
It depicts God, bloodied and carrying a gun, under the headline: "One year on: The assassin still at large."
The head of the Christian Democrat Party, Christine Boutin, said on Twitter: "The front page of the Charlie Hebdo anniversary. What is it referring to? Religions?
"It's becoming an obsession. This tragedy deserved better."
The special edition, which goes on sale on Wednesday, will feature cartoons from those who died in the attacks on the Charlie Hebdo offices, reports the BBC's Lucy Williamson in Paris.
Cartoonist Laurent Sourisseau (Riss), who was seriously injured in the violence, drew the anniversary front cover and has written an angry editorial in defence of secularism.
He reportedly blames the 7 January attack on the magazine on Islamist fundamentalists, organised religion, and intelligence failures.
He says Islamist fanatics and other religious zealots wanted Charlie Hebdo to pay the ultimate price "for daring to laugh at religion".
Subscriptions to the magazine shot up in the weeks following the attacks.
But in the past few months senior cartoonist, Luz, and columnist Patrick Pelloux have announced their resignations, amid disputes over how to manage donations, and challenges to the paper's new editorial team.