To a midnight showing of the new Batman film at a movie theatre in Aurora, Colorado, James E. Holmes carried a .223-calibre Smith & Wesson AR-15 assault-style rifle, a Remington twelve-gauge shotgun, and a .40-caliber Glock handgun; a second Glock was found in his car. He had a magazine for the AR-15 that would have allowed him to shoot a hundred bullets before reloading. He had bought more than six thousand rounds of ammunition online. He dressed in black, with a tactical vest and helmet, and wore a gas mask. He had dyed his hair red. He is thought to have shot seventy people; twelve have died. As a neuroscience graduate student at the University of Colorado, Holmes had been studying the genesis of madness. He reportedly told police that he was the Joker.

No one expects this massacre to lead to a reform of the nation’s gun laws. “No guns,” Batman says to Catwoman, in “The Dark Knight Rises.” That’s more than will likely be said on the floor of Congress.

As I wrote in the magazine in April, there are nearly three hundred million privately owned firearms in the United States: a hundred and five million rifles, eighty-three million shotguns, and a hundred and six million handguns. In no other country in the world is there a rate of civilian gun ownership approaching that in the U.S.: a gun for every American. Nevertheless, aside from Mayor Michael Bloomberg, of New York, almost no one holding or running for public office today is willing to talk about guns, except to argue for Americans’ constitutional right to own them.

It hasn’t always been this way. Americans used to hold a different set of beliefs about guns. So did Batman, who started out with a gun—until he got rid of it. The nineteen-thirties, the golden age of comic-book superheroes, was a time of landmark gun legislation. In 1934, the National Rifle Association supported the National Firearms Act—the first federal gun-control legislation—and, four years later, the 1938 Federal Firearms Act. A great many gun-safety measures on the books today date to those two pieces of legislation, which together mandated licensing for handgun dealers, introduced waiting periods for handgun buyers, required permits for anyone wishing to carry a concealed weapon, and effectively prohibited the sale of the only gun banned in the United States today: the automatic weapon (or “machine gun”).

In 1939, the constitutionality of the National Firearms Act was brought before the U.S. Supreme Court, in U.S. v. Miller. A ruling issued on May 15, 1939, upheld the law, unanimously, and uncontroversially.

The same month the court issued its ruling in Miller, Batman, written by a cartoonist named Bob Kane, began appearing in Detective Comics (later known as DC Comics). Superheroes were new, but they were already controversial; by the spring of 1940, critics were calling comic books a “national menace.”

In the eighteenth century, critics thought reading novels would corrupt girls’ morals. In the nineteenth century, mystery fiction was suspected of causing crime. In the twentieth century, the pulp-fiction panic had to do with comic books and juvenile delinquency. Walter Ong would argue that Mickey Mouse was evidence of creeping secularism and Superman of rampant fascism. In the nineteen-fifties, there would be hearings in Congress after Fredric Wertham, a New York psychiatrist, published a polemic blaming comics for everything from truancy to murder. (Batman was singled out for homosexuality. Wertham wrote of one of his violent thirteen-year-old patients, “Like many other homoerotically inclined children, he was a special devotee of Batman.”) But in the nineteen-thirties, the problem with Batman was Batman’s gun.

In a story published in October of 1939, Batman used a handgun to shoot a vampire—silver bullets to the heart. He used a gun again in the next episode, to fire some shots at two evil henchmen.

At the time, Detective Comics had just hired a new editorial director, a guy from Brooklyn named Whitney Ellsworth. (Not long after hiring Ellsworth, Detective Comics established an editorial advisory board, consisting of people like psychologists and English professors.) When Kane submitted his next story, Batman was shooting again. “Ellsworth said to take the gun out,” Kane remembered.

Maybe it was a simple demurral to the critics, but the disarming of the Dark Knight reads like a concern about the commonweal, a deferral to an accepted and important idea about the division between civilian and military life. Superheroes weren’t soldiers or policemen. They were private citizens. They shouldn’t carry concealed weapons. Villains carried guns. The Joker, introduced in the spring of 1940, carried a gun, and sometimes two. (Batman thwarts him with a bulletproof vest; once Joker realizes this, he aims for his head.) After Ellsworth told Kane to lay off the guns, Kane wrote a two-page piece—issued in November, 1939—explaining Batman’s origins: “Legend: The Bat Man and How He Came to Be.” When Bruce Wayne was a boy, his parents had been killed before his eyes, shot to death.