The two Islamist gunmen killed chief editor and cartoonist Charb, along with staffers Cabu, Honoré, Tignous and Wolinski, Bernard Maris, Elsa Cayat and Mustapha Ourrad, along with guest Michel Renaud and maintenance worker Frédéric Boisseau. Two police officers, Franck Brinsolaro and Ahmed Merabet, were also killed and eleven wounded – four seriously.
Then President François Hollande called the assault a "terrorist attack of the most extreme barbarity".
The gunmen, Saïd and Chérif Kouachi, were French Muslim brothers of Algerian descent. They were shot and killed by police after a two-day manhunt, but many still wonder what impact the attack is having today.
Time to move on?
Charlie Hebdo says many people have grown tired of the story. "Four years on, many people are already weary of it," says an editorial in the satirical weekly published on Saturday.
"Haven't you finished with that tale?" – one of questions sometimes put to Charlie Hebdo staff, according to cartoonist Riss (Laurent Sourisseau), one of the journalists who survived the attack. Or, "Perhaps you should move on!"
Riss also reports comments on social media, saying, "I thought he'd been killed," referring to one of the current team.
The editorial says behind this "apparent "indifference" is a worrying trend, that shows populism and religion "returning to political life". It says the principles of enlightenment, the age of reason, are under attack.
The front of the 5 January 2019 issue features a Catholic priest and an imam blowing out a candle, and the text "the return of anti-enlightenment."
Critics say that freedom of speech has come increasingly under attack since the Charlie Hebdo murders.
Some point out that after the "Je suis Charlie" protests – the slogan used to show solidarity with victims and support for press freedom – faded away, some even blamed the magazine for the attacks.
Glenn Greenwald, of The Intercept, the magazine that helped NSA Whistleblower Edward Snowden to publish his revelations about global snooping of the US intelligence agency, pointed out just months after the attack, in April 2015, that 204 PEN writers had objected in a signed letter against bestowing Charlie Hebdo with an award.
The letter said, "There is a critical difference between staunchly supporting expression that violates the acceptable, and enthusiastically rewarding such expression." It expressed concern that "by bestowing the Toni and James C. Goodale Freedom of Expression Courage Award on Charlie Hebdo, PEN is not simply conveying support for freedom of expression, but also valorizing selectively offensive material: material that intensifies the anti-Islamic, anti-Maghreb, anti-Arab sentiments already prevalent in the Western world."
Accomplice arrested after four years
In late December 2018, an accomplice of the Kouachi brothers was arrested.
Peter Cherif, 36, was close to the brothers, and suspected of being one of the masterminds of the 2015 attack.
French authorities had been seeking him since he disappeared in 2011 on the final day of his trial in Paris for fighting in Iraq alongside Al-Qaeda in 2004.
Cherif, who was sentenced to five years in prison in the trial, was arrested on 16 December in Djibouti after arriving from Yemen carrying fake ID.
He appeared before a French judge on 27 December and was charged with "terrorist conspiracy" before being returned to prison to serve a five-year sentence from his original trial.
Prosecutors have said he is not currently being held in connection with the Charlie Hebdo attack.
In 2017, investigators opened a new line of inquiry into his activities in Yemen where he joined the senior ranks of the local branch of Al-Qaeda known as AQAP, according to a source close to the case.
His wife, “Soulef A”, who was was arrested alongside Cherif and their two children in Djibouti, has been charged with "criminal association with terrorists" and "financing a terrorist enterprise", and held pending a hearing on 7 January, according to France 24.
Just a week after Cherif's arrest, judicial sources told AFP that French prosecutors were calling for 14 people to be tried in connection with Charlie Hebdo murders.
It will be up to anti-terrorist judges to decide whether all 14 are tried.
Those likely to face trial are accused of "complicity" in assisting the attackers, including providing them with weapons.