Lucas Jackson / REUTERS Signs, balloons, packages of Skittles candies and cans of iced tea are piled into a memorial dedicated to Trayvon Martin near the site where he was killed in front of The Retreat at Twin Lakes community in Sanford, Florida, March 27, 2012.

Florida’s controversial “Stand Your Ground” law wasn’t always so controversial. The law, which gives citizens the right to use deadly force if they “reasonably believe” they are in danger, has been the subject of national scrutiny in the wake of Trayvon Martin’s death. But the statute former Governor Jeb Bush signed in April 2005 enjoyed broad bipartisan support in the Sunshine State legislature. It sailed through the Senate unanimously, 39-0, and faced only token Democratic opposition in the House, where it passed 94-20.

The statute’s success was partly a function of propitious timing. In 2005, Florida had just been racked by post-hurricane looting, including the incident the bill’s architects cite as their inspiration, in which an elderly man shot and killed a burglar who broke into his RV. The man was left in legal limbo, says Dennis Baxley, the Florida Republican who sponsored the House bill, as authorities wrestled with whether his actions were protected by the so-called Castle Doctrine, a theory derived from English common law that permits property owners to use force to defend themselves in their own homes. “We wanted citizens to know that if they are attacked, the presumption will be with them, and we will empower them to stop a violent act from occurring,” Baxley says. By his telling, Stand Your Ground was an effort to codify those protections.

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It was also a new frontier in the NRA’s crusade to expand Castle Doctrine laws beyond gun-owners homes and into public spaces. Florida has long been friendly territory for the NRA. In 1987, it passed landmark concealed-carry legislation that allowed anyone who met modest criteria earn a permit to tote a concealed weapon. It was this statute, gun-control activists point out, that helped George Zimmerman, the 28-year-man who shot the unarmed Martin, 17, obtain a permit to carry a gun despite a record that includes an arrest for battery on a law-enforcement official in 2005.

Florida was ground zero for the NRA’s quest to enhance the Castle Doctrine. As a large and diverse swing state, it carries symbolic weight as a barometer of public opinion. But it is also a state where the gun-rights lobby is a formidable force. Gun-control activists trace this potency to Marion Hammer, a tiny, gray-haired septuagenarian who has been at the forefront of the gun-rights movement for decades. The NRA’s former president — the first female head in the organization’s history — Hammer is now a lobbyist based in Tallahassee. Gun-control proponents say she kick-started Stand Your Ground’s journey through the legislature and wielded her clout to pressure skittish lawmakers into backing the bill. “Her sway in the Florida legislature has been instrumental for the NRA,” says Brian Malte, director of legislation at the Brady Campaign to Prevent Gun Violence. “It’s why the NRA has used Florida as its laboratory.” (Hammer did not respond to an interview request from TIME.)

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As planned, the law spread from there. In the seven years since Stand Your Ground became law in Florida, a wave of similar measures have swept across the U.S. According to the Legal Community Against Violence, 24 states in addition to Florida now have Stand Your Ground (or, in the gun-control lobby’s parlance, “Shoot First” or “Make My Day”) laws. In some of those states, gun-owners still have a duty to “retreat” — to avoid violent confrontation if possible — outside their homes. But in some states, like Florida, the law contains no such provision. “Florida was their testing ground,” says Malte, “and what the NRA has done is they’ve tried to nationalize Florida’s law.”

To expand the doctrine of Stand Your Ground, the NRA harnessed its connections with an organization called the American Legislative Exchange Council (ALEC), which promotes conservative public policy by affecting change in state legislatures. One of the ways ALEC does this is to draft model legislation that its members can push in their home states. According to gun-control proponents, ALEC used Florida’s Stand Your Ground law as a template in its push to broaden the Castle Doctrine nationwide. “The fact that ALEC made it their model immediately improved the law’s chances of being passed in other states,” says Ladd Everitt of the Coalition to Stop Gun Violence. “It exponentially increased their ability to spread it around the country.” ALEC did not respond to an interview request, but as the liberal group Media Matters points out, in 2008 one of its residents acknowledged that the group had worked in tandem with the NRA to advance the Castle Doctrine, “one of our model bills that we have states introduce.”

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The bill that triggered copycats elsewhere has had significant consequences for Florida. According to a Tampa Bay Times analysis of public records and newspaper clips, Stand Your Ground has been invoked at least 130 times since its passage in 2005, including a dramatic spike during the past 18 months. In more than 70% of Stand Your Ground cases, it was used as self-defense in a fatality. In at least 50 cases, prosecutors declined to bring charges. Another nine defendants were given immunity in court, while nine more saw their charges dismissed. In Florida, claims of justifiable homicide in Florida have tripled since the law’s passage in 2005. Martin’s death, while tragic, “is nothing new,” says Everitt. Indeed, the law has generated its share of horror stories. What is new, however, is the national attention and the decibel of the outrage. “I felt like I was watching American history unfold,” Everitt says. “The heat on this thing is unlike anything I’ve seen. It’s not just outrage over Trayvon. It’s people connecting his death to a bad gun law. We didn’t see that after Virginia Tech. We didn’t even see that after Tucson.”

To Baxley, the original sponsor of Stand Your Ground, the proliferation of cases in which the law has been invoked “could be a confirmation that the policy is working.” He says Stand Your Ground has “empowered people to stop violent acts. It has saved lives.” As Baxley notes, proponents of Stand Your Ground profess concerns about its “inaccurate application to a very tragic and seemingly senseless death.” Zimmerman’s own lawyer has shrugged off suggestions that he could invoke Stand Your Ground as a defense. “The law does not apply to this particular circumstance,” Bush said last week, as the outrage over Martin’s death built toward a crescendo. “Stand your ground means stand your ground. It doesn’t mean chase after somebody who’s turned their back.”

As for the NRA, it has yet to stake out a stance on the issue. Andrew Arulanandam, the organization’s director of public affairs, declined comment when reached by TIME. “On the one hand, it appears the Stand Your Ground law doesn’t apply,” he says, “but we don’t know exactly what happened yet.” Of course, disavowing Zimmerman as a rogue vigilante would be a good way to deflect attention from the law itself.

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