Why would terrorists kill cartoonists?

The attack is horrifying no matter what way you look at it, but it's almost bewildering when you consider the target. The attackers weren't fighting the French state. They weren't killing soldiers and appear to have only incidentally killed policemen. They weren't even attacking a far-right group that pushes an anti-Islam line.

Instead, they were targeting satirists and cartoonists, such as the newspaper's editor, Stéphane Charbonnier, and Jean Cabut, better known as Cabu. The terrorists wanted to kill people who make drawings for a living.

Stranger still, that doesn't even seem that unusual. Charlie Hebdo had been targeted before. In 2012, its offices were firebombed and its Web site was hacked. While no one was harmed, the perpetrators were never caught. It was widely assumed that the attacks were committed by extremist Islamists.

Then there's the case of Kurt Westergaard, a Dutch cartoonist who was the subject of a murder plot in 2008. Or the case of Swedish artist Lars Vilks, who received death threats and was the subject of a number of assassination attempts after a drawing of his was published in the Swedish newspaper Nerikes Allehanda.

In each case, the threats stemmed from controversial depictions of the Muslim prophet Muhammad. Graphic depictions of the prophet are considered taboo by many Muslims, in particular Sunni Muslims, largely because they could be considered a form of idolatry (similar traditions have existed in a number of faiths). Blasphemy against the prophet is a considered a crime (sabb al-nabi), though religious teaching on how it should be punished varies widely: As noted in "Muhammad in History, Thought, and Culture: An Encyclopedia of the Prophet of God," Koranic verses can be interpreted to suggest that any punishment should be meted out by God, not by humans.

Depictions of Muhammad by non-Muslims have caused offense for centuries, whether in Dante's "Divine Comedy" (where the Islamic prophet is depicted in hell), or in a statue of Muhammad that had stood on the roof of New York City's State Appellate Division courthouse for 50 years (it was removed in 1955 after protests from Islamic countries, though a depiction in the U.S. Supreme Court in Washington remains). In 1977, a film about the life of Muhammad titled "The Message" attempted to avoid the problem by never actually showing the prophet. It didn't work: After Islamic groups took hostages in a Washington siege that left two dead, the filmmakers canceled the Washington premiere and halted screenings.

However, in the past few years the issue of depiction of Muhammad has intertwined with debates about free speech, with cartoonists often leading the charge. In 2005, the Dutch newspaper Jyllands-Posten asked illustrators if they would be willing to draw Muhammad after writer Kare Bluitgen said he was unable to find anyone to illustrate his book on the prophet. The challenge was also, in part, a response to the murder of Theo van Gogh, a filmmaker who was killed by an extremist in 2004 after the release of his short film "Submission," which criticized how Islam treats women.

In the end, 12 cartoons showing Muhammad were published by Jyllands-Posten, including one by Westergaard that showed the prophet wearing a bomb as a turban. The publication of the cartoons sparked controversy among Dutch Muslims, who said the action was designed specifically to insult Islam. It soon spiraled into an international incident. The 57-nation Organization of the Islamic Conference issued a statement condemning the cartoons, and Saudi Arabia withdrew its ambassador to the Netherlands.

However, there was also significant support for Jyllands-Posten. One Dutch poll showed that 62 percent of those surveyed said the paper should not apologize. Newspapers all around the world began to republish the cartoons, saying they supported a fight against self-censorship, and faced their own backlash. Other cartoonists, inspired by the controversy, began to draw similar images: Gregorius Nekschot, a pseudonymous Dutch cartoonist, received both support and criticism for his own cartoons regarding Islam (he was arrested for "insulting people" in 2008). Swedish artist Vilks drew a picture of Muhammad as a type of street sculpture called a roundabout dog in 2007; after it was withdrawn from a local art exhibition, it went on to be published in newspapers and provoked another round of outrage and threats.

In 2010, in response to threats made against the creators of the U.S. cartoon show "South Park," which had repeatedly shown Muhammad, cartoonist Molly Norris declared May 20 "Everybody draw Muhammad" day in an illustration of her own. Norris herself decided not to draw Muhammad on the day. "Fight for the right to draw Muhammad, then decline doing so," she explained at the time. And in 2012, the satirical newspaper the Onion published an article that showed Moses, Jesus Christ, Ganesha and Buddha engaged in a sexual act. "No One Murdered Because Of This Image," the headline read.

Charlie Hebdo, an irreverent weekly that had a history of mocking just about every religion and ideology, placed itself at the center of the debate. In 2007, it republished the Jyllands-Posten cartoons and added one of its own. In 2011, it published a number of images of Muhammad and renamed itself Charia Hebdo, a play on the word "sharia," for an issue. After its offices were firebombed in 2012, it published yet more cartoons showing Muhammad. In a country with an often turbulent history of relations with the Islamic world and France's own Muslim minority, it was provocative. Writing in the Financial Times after Wednesday's killings, Tony Barber said the newspaper needed some "common sense."

Regardless, the attempts by a small minority of Islamist extremists to kill cartoonists are strikingly illogical. Even if the cartoons are insulting to many Muslims (including the vast majority who don't support today's violence), there are far greater injustices and outrages in the Muslim world that surely merit more attention.

So why cartoons? The ability of the Internet to spread anger likely plays a part: It allows media to spread quickly and internationally, often without much context. It was a terribly made, low-budget film shot in California that almost no one had ever seen ("The Innocence of Muslims") that sparked huge protests across the Middle East in 2012 after appearing on YouTube, for example.