When a Molotov cocktail was thrown into the offices of the satirical weekly Charlie Hebdo, setting the premises on fire, three years ago in the early hours of a Wednesday morning, no one at the newspaper thought for a moment to prevent the distribution of that week’s edition, fresh copies of which were making their way to news stands around France. There was no doubt, the reason for the arson attack was the advance notice that the edition would be titled Charia Hebdo, a word play on the name of the paper and sharia, Islamic religious law, and would be dedicated to jokes and cartoons at the expense of the Prophet and his followers. On the cover was a drawing of Mohammed saying – “one hundred lashes if you don’t die of laughter.”

Today. Again, a Wednesday. A terrorist massacre at the relocated Charlie Hebdo offices. News organizations around the world rushed to provide live reports on their websites and television channels, but refrained from showing the cartoons for which 10 journalists and two police officers lost their lives. Instead they aired the footage of one of the shooters finishing off a dying officer from close-range. The caricatures of Mohammed were hidden behind obscuring pixels.

It is still unclear to which movement the Paris attackers belonged. But their message was loud and clear. Any editor will now think a hundred times before endangering his or her employees and in most cases, simply prefer a less offensive alternative. Until recently the danger was mainly local fanatics who would, at worst, throw a shoddily constructed Molotov cocktail – but this attack was carried out by well-armed and trained professionals. In the footage two of the attackers are seen emerging from the building, not running, not shooting wildly in every direction. When the officer appears down the street, they shoot a few well-aimed bullets, proceed carefully towards the figure on the ground and shoot once more. Unhurried, they get back into a black Citroen and drive away without breaking the speed-limit.

This is the third case in the last three years in which French jihadists - assuming the culprits are indeed jihadists in this case too - have gone on a shooting spree. Mohammed Merah, who killed three soldiers and four Jews in Toulouse in 2012, was traced to his home by police only after he called a local radio station to brag. Mehdi Nemmouche who crossed the border and murdered four at the Jewish Museum in Brussels, was caught only because he chose to return on a bus line routinely searched for drugs and was enough of an amateur to hold on to the murder weapon. This time they’re professionals.

They arrived fully armed and equipped – one of them with combat webbing holding Kalashnikov magazines. They moved carefully down the street, maintaining eye contact, and shot with discipline. They carried out advance surveillance, knew how to overcome the security systems and to arrive during the weekly editorial meetings when all the journalists, including the cartoonists they had targeted for insulting the prophet, would be present.

This is the double nightmare of Western security services. Trained jihadist terrorists, with Mideastern experience; native Europeans moving freely on the continent and speaking the local lingo. Now, after escaping the scene without being identified, they have gone to ground in a city of 12 million.

French intelligence, like their colleagues across Europe, have been looking for ways to prepare for the return of the homegrown jihadists, returning from their time in Syria or Iraq with Al Qaida, Al Nusra or ISIS, also known as Islamic Front. Over the last few months, the monitoring of these prodigal sons and daughters has improved. Some have been arrested, others questioned and warned and the networks which enlist and help them travel east have been dismantled. And still, despite the French security services’ readiness to use invasive methods to listen in on mobile phones and search other electronic communications, this cell, which must have spent weeks if not months preparing the attack, succeeded in maintaining operational security and did not sound an alarm.

The most difficult dilemma, similar to that of the authorities in Boston following the marathon attack two years ago, is whether to shut down a mega–city until the cell is captured or allow life to go on at the risk of another attack. Even after the murderers are run to ground, the dilemmas will remain. How to deal with terror cells of native Frenchmen? In recent weeks there has been a series of attacks in France, using vehicles, knives and even shootings which have been explained away as the actions of deranged individuals. This time there is no doubt as to the motive.

Three years ago, the edition that came out the week after the Molotov attack, featured a cartoon of a religious Muslim French-kissing a secular cartoonist, pencil behind his ear, under the title “Love is stronger than hate.” That’s a lovely sentiment, but to face the current threat, love will probably not be enough.