There were some 22,000 people in the crowd at the Route 91 Harvest Festival in Las Vegas Sunday night when the gunman started firing. By the time police reached Stephen Paddock’s sniper’s perch on the 32nd floor of the nearby Mandalay Bay Resort and Casino, more than 500 people had been injured and at least 59 were killed, making it the deadliest mass shooting in recent U.S. history.

As law enforcement works to understand how and why this could have happened, a central question for those directly affected will be what, if any, legal recourse do they have? While legal experts say there are a range of entities who could find themselves liable — including the estate of the gunman himself — one group is all but off-limits: the manufacturers of the weapons used in the attack. The reason is a tangled web of lawsuits, legislation and lobbying.

Starting in the 1980s, plaintiffs began to file civil claims against gun manufacturers and retail stores after violent incidents, winning some notable victories. In 1997, for example, the Florida Supreme Court upheld a jury verdict that found Kmart liable for selling a gun to an intoxicated person, who later shot his girlfriend, leaving her permanently quadriplegic. According to Timothy Lytton, a professor of law at Georgia State University and editor of the book Suing the Gun Industry, over thirty municipalities and the State of New York filed suits against the firearms industry to recoup costs of emergency personnel responding to shooting incidents. In 2000, Smith & Wesson reached a settlement agreement with the U.S. Department of Housing and Urban Development and the Treasury Department in which the gun maker promised to implement safety enhancements (all firearms subject to drop test to insure they do not go off when dropped) and follow a code of conduct in its sales and distribution practices (manufacturers sell only to authorized dealers; make gun show sales only after the buyer completes a background check).

Read more: These Are the Victims of the Las Vegas Shooting

This flurry of litigation coincided with the 1998 Tobacco Settlement agreement, in which the four biggest tobacco companies agreed to pay $206 million over 25 years to the states. The settlement spooked gun manufacturers, who feared they could be vulnerable to a similar coordinated legal assault. As a result, they leaned on Congress for insulation. “The industry didn’t just want to win cases,” says Heidi Li Feldman, a professor of law at Georgetown University. “They wanted to make it impossible for them to be held accountable through tort litigation.”

In 2005, the firearms industry won what remains one of its most important legal victories: the passage, under a Republican-controlled Congress, of the Protection of Lawful Commerce in Arms Act, or PLCAA. In effect, the act shields gun manufacturers and sellers from civil claims brought by victims of gun violence.

“It’s shocking that this law exists,” says Avery Gardiner, co-president of the Brady Center to Prevent Gun Violence, which advocates for stronger restrictions on guns. “We need to ask ourselves, why should special provisions be given to the gun industry?”

Wayne LaPierre, the longtime head of the National Rifle Association, said at the time of its passage that the law was necessary to keep the firearms industry solvent and called it “the most significant piece of pro-gun legislation in 20 years.”

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There are some exemptions under PLCAA. If a defective product causes death or injury, or a manufacturer or dealer violates state or federal law in the sale or marketing of a product, plaintiffs can bring a suit. The most critical exemption that has been tested in court is the common law concept of “negligent entrustment.” The idea is that a gun can’t be sold to a person if the seller knows, or reasonably should know, that the buyer poses an unusually high risk of misusing the weapon.

That exemption was at the heart of a 2015 case in Milwaukee, when a civil jury awarded $5 million to two police officers shot by a teen. Jurors found a gun shop negligent for selling the gun to a “straw purchaser” who passed the firearm to a person too young to legally own a gun. (The case was ultimately settled for $1 million: on a federal form, the buyer indicated he was purchasing the gun for someone else. On the state form, he said he was buying it for himself. That discrepancy, the court found, should have aroused reasonable suspicion, and stopped the sale).

In another case last year, Odessa Gun & Pawn in Missouri reached a $2.2 million settlement with a woman who claimed the store was negligent in selling a firearm to her mentally-ill adult daughter, who shot and killed her father. Defense attorneys tried to get the case dismissed based on PLCAA; the Missouri Supreme Court permitted it to proceed.

Collecting damages from gun manufacturers, however, is significantly harder under PLCAA than proving retailers negligent. That’s because negligent entrustment tends to apply to one-on-one interaction. “You need that personal relationship,” says Patrick Dunphy, a plaintiff’s attorney who worked on the Milwaukee police case. Manufacturers rarely sell guns straight to consumers off the factory floor.

After the Sandy Hook school shooting in Newtown, Conn., some families of the victims tried to extend the negligent entrustment exemption to manufacturers, filing a civil suit against Remington Outdoor Co., the maker of the rifle used in the massacre, as well as against the dealer and the owner of the store in which the shooter’s mother purchased the assault rifle. The families argued that manufacturers should know marketing a weapon originally designed for combat to the general public creates an unreasonable risk that the weapon will be misused. “The plaintiffs tried to analogize individual interaction to the collective situation,” says Feldman.

A judge dismissed the case last October, citing PLCAA. The case is under appeal.

Victims in Las Vegas will be up against similar legal constraints. “No plaintiff has ever prevailed in any of these lawsuits against gun manufacturers,” says Lytton.

Stephen Paddock, the man police identified as the shooter, reportedly had 23 firearms in his hotel room and officials found 19 more at his house. Two Nevada gun shops confirmed Monday that they sold firearms to Paddock in the last year. They said he passed all background checks, though it’s unknown if he used those specific firearms in the Las Vegas massacre.

For supporters of stronger firearms restrictions, repealing PLCAA is a priority. “If you significantly take away access to the courts, you take away a tool in the toolbox to make sure companies conform to social norms,” says Gardiner. “When a company does something that has a negative effect on everyone else, we want them to be forced to pay for it.”

Dunphy, the Wisconsin attorney, isn’t so hopeful. “If Sandy Hook didn’t result in legislation that either eliminated or restricted the type of guns that can be sold, or the people to whom they can be sold, nothing will ever change,” he says. “When someone slaughtering kids in a grade school isn’t enough, what is?”

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Write to Sean Gregory at sean.gregory@time.com.