I can see you didn't read the article either....

"The AR-15 did not immediately pop as a mass-market gun. It was introduced to civilians in the early 1960s, when Colt's "AR-15 Sporter" was pitched as a "superb hunting partner." But the rifle – tarnished by its association with America's deadly misadventure in Vietnam – didn't prove popular with the gun-buying public until this century, when production soared from 60,500 in 2001 to 1.27 million in 2012."

"The boom was ignited by the expiration of the federal assault-weapons ban in 2004. The ban, enacted by President Bill Clinton, had done little to limit the deadliness of the AR-15; John Allen Muhammad and Lee Boyd Malvo, the D.C. snipers, wielded a "ban-compliant" Bushmaster in 2002. But the law had blocked sale of militarized upgrades – ranging from 30-round magazines to flash suppressors and grenade launchers. "The end of the assault-weapons ban," says Josh Sugarmann, executive director of the Violence Policy Center, "allowed for the customization and modification of these weapons to make them look even more militaristic, even more grand in the eyes of their owners.""

"The following year, amid a $1.7 million lobbying blitz by the NRA, Congress passed a sweeping change to American gun law. The Protection of Lawful Commerce in Arms Act (PLCAA), signed by President George W. Bush, provides gun manufacturers with near-total liability protection for the criminal misuse of their products. "The perception for the gun industry is: 'We can't get sued,'" says Josh Koskoff, a Connecticut attorney who filed a case on behalf of Newtown families. "'We can be as unethical and as wild and aggressive in the marketing as we want.'" (The industry's trade group, the NSSF, declined to comment.)"