NRA Executive Vice President Wayne LaPierre testified at the Senate hearing on gun violence Wednesday. He argued that law-abiding gun owners should not be blamed for acts of violence by deranged criminals. (Jayne Orenstein/The Washington Post)

A legal shield written by Congress to benefit the firearms industry is posing unexpected hurdles for parents in Newtown, Conn., and victims of other mass shootings, who want to use the courts to hold gun makers accountable and push them to adopt stricter safety standards.

The law, approved in 2005 after intense lobbying by the National Rifle Association, grants gun companies rare protection from the kind of liability suits that have targeted many other consumer product manufacturers.

It was introduced amid a wave of lawsuits brought by city governments, which argued that gun companies had created a “public nuisance” by encouraging the proliferation of weapons. Advocates for gun makers said such suits threatened to destroy the industry and imperil Americans’ constitutional right to bear arms.

But over the past eight years, the legal shield has increasingly been used to block a different stripe of legal action — suits brought by victims and their families alleging that gun makers had failed to equip their firearms with proper safeguards or that gun dealers sold weapons improperly.

Attorneys for victims of mass shootings, such as the massacre Dec. 14 at Sandy Hook Elementary School in Newtown and last summer’s rampage in an Aurora, Colo., movie theater, say they have been surprised by the legal constraints they would face in challenging the gun industry.

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“It makes no logical sense. . . . If their wallets were threatened, they would have a greater interest in making firearms safer,” said Veronique Pozner, whose 6-year-old son, Noah, was one of the 20 children killed at Sandy Hook.

Pozner, who has been eyeing a lawsuit, has been discussing the gun industry’s protections with a lawyer she and other Newtown parents recently retained. “I am looking at anything that can be done to prevent this from happening to another family,” she said in an interview this week, describing the searing memories of her fallen son. “I don’t want his life to be a statistical blip.” Pozner said she wants to press the maker of the semiautomatic rifle used in the crime, alleging it failed to install a high-tech safety device that might have prevented Adam Lanza from firing the gun, which he took from his mother.

Marc Bern, a New York trial lawyer representing family members of Aurora victims, said the gun law severely limited his clients’ options. He is pursuing a case against the movie theater company, although some of his clients had expressed interest in trying to pursue companies that provided guns or ammunition to the shooter.

“We looked at the gun industry, but they were able to insulate themselves with this law,” Bern said. “It is absolutely outrageous that the gun industry is not accountable when virtually every other industry in this country is accountable.”

Officials from the NRA and the gun industry defend the law as necessary to protect U.S. companies from costly, and what they see as unfair, litigation that seeks to blame manufacturers and sellers for crimes they did not commit.

Attorneys for victims in Newtown and other recent shootings, however, say they do not necessarily seek to hold gunmakers liable because a gun was used to commit a crime.

These lawyers say they are seeking safety improvements, like those that resulted from decades of suits against the auto industry, which argued that car makers could be liable for damages if they failed to adopt feasible safety measures. And just as legal action helped lead automakers to add seat belts and air bags, potential litigants in gun cases say they want firearms makers to add readily available safety features, such as biometric locks that would allow a gun to be fired only by its licensed owner.

Yet when plaintiffs have brought a variety of lawsuits against gun companies and dealers, they have run up against the industry’s unusual liability shield.

In 2009, for instance, the Illinois Supreme Court rejected claims by the family of a child killed by his 13-year-old friend, who was playing with his father’s loaded Beretta 9mm pistol. The family argued that the gun’s design was flawed because the device meant to register ammunition in the chamber was inadequate and that the company should be held responsible. But the court ruled that the company was protected by the industry’s legal shield.

Now, the massacre at Sandy Hook is focusing new attention on the gun liability law, called the Protection of Lawful Commerce in Arms Act. Some Democrats in Congress are pushing legislation, sponsored by Rep. Adam B. Schiff (Calif.), to roll back the law and make it easier for suits against the gun industry to proceed.

Lawrence G. Keane, general counsel of the Newtown-based National Shooting Sports Foundation, the industry’s trade organization, noted that Congress adopted the law with “overwhelming” majorities and predicted that any repeal effort would fizzle.

“It’s not going to happen,” said Keane, who lobbied for the shield and displays a picture of President George W. Bush signing the law on the wall of his office, just a few miles from Sandy Hook. “Suing law-abiding firearms manufacturers for the criminal misuse by third parties of firearms that were lawfully sold amounts to suing Ford for drunk-driving accidents.”

The law prohibits suits against gun dealers and manufacturers “for the harm caused by those who criminally or unlawfully misuse firearm products.” It applies not only to federal courts, but also actions at the state and local levels.

Although far-reaching, the law allows liability suits to proceed in rare cases where a manufacturer or seller knowingly broke federal laws governing the sale and marketing of guns and in cases involving an alleged defect in the design or manufacture of the weapon, such as a malfunctioning trigger.

Advocates for gun companies say the law is working properly if it is thwarting suits that seek to find fault with law-abiding gun sellers or makers.

“Since its enactment, we have seen state and federal courts across the country dismiss personal injury and wrongful death lawsuits arising out of criminal or unlawful firearm use because it is simply unfair to hold manufacturers and distributors responsible for the wrongful acts of others,” said Craig A. Livingston, a California lawyer who has represented gun manufacturers, including Beretta in the Illinois case. “While legitimate product liability suits are being allowed to proceed, those in which an injury or death was caused by the intentional discharge of a firearm are not. That is exactly how Congress drew it up.”

The NRA played a major role in securing passage of the law, besting other influential groups such as the American Bar Association, which had argued that the measure would infringe on the traditional right of Americans to seek redress in the courts.

At the time of its passage, NRA Executive Vice President Wayne LaPierre called the measure “the most significant piece of pro-gun legislation in 20 years,” adding that “history will show that this law helped save the American firearms industry from collapse under the burden of these ruinous and politically motivated lawsuits.”

The vote in Congress came after a years-long effort by the NRA and its allies. The campaign drew on the support of the Bush administration, which weighed in with a White House memo backing the law as crucial to the economic well-being of an important industry and a letter from a top Pentagon lawyer saying the measure would help “safeguard our national security by limiting unnecessary lawsuits against an industry that plays a critical role in meeting the procurement needs of our men and women in uniform.”

The liability exemption sets firearms apart from nearly every other industry. A handful of products have been granted limited immunity. Vaccine makers, for instance, have certain protections against suits from injured patients. Internet service providers are shielded from many suits over defamation or copyright infringement.

Legal scholars say the breadth of the protections granted to the gun industry is rare for consumer product manufacturers.

“To give a product manufacturing industry a substantial immunity is really distinctive,” said Robert L. Rabin, a Stanford University law professor who specializes in product liability cases. “The auto industry, the home supply industry, none of the industries that manufacture products that are ubiquitous in the market have that sort of insulation from liability.”

John Goldberg, a Harvard Law School professor who specializes in product liability, said the gun industry protections, although unusual, did not reflect a “dramatic taking away” of consumers’ rights. The success of safety-related lawsuits involving third-party crimes was never assured, he said.

“If you didn’t have this statute, would the plaintiffs always win? I don’t think so,” Goldberg said.

The constitutionality of the liability shield is being tested in a case pending before the Alaska Supreme Court, alleging that a gun store in Juneau should be held liable for the death of a shooting victim. In this case, family members of the victim say the store erred because the shooter, a drifter, left cash on the counter and then took the gun from the store without undergoing a required background check.

Jonathan Lowy, director of the Brady Campaign to Prevent Gun Violence’s Legal Action Project, who is arguing the Alaska case, says the lawsuit claims in part that the legal shield is unconstitutional because it infringes on the rights of state courts. The Obama administration, which has tangled with the NRA and the firearms industry over gun control, has filed a brief supporting the constitutionality of the legal shield’s reach at the state level, citing the Interstate Commerce Clause.

Lowy said lawyers have to be creative in finding legal strategies to get around the shield. “You have to dig in the weeds to see there are still ways to bring causes of action,” he said.

In a case involving a white supremacist who used a pair of guns to shoot up a Jewish community center and the surrounding neighborhood in Los Angeles in 1999, a court dismissed the case brought by the family of one victim, a postal worker, against Glock, the U.S.-licensed maker of the pistol used to kill him.

But four other victims, who survived, were able to press a lawsuit. They are suing a separate company, which produced the 9mm semiautomatic rifle used against them. The case was allowed to proceed because the Chinese manufacturer had no U.S. license and was not covered by the legal shield.

Alice Crites contributed to this report.