The reason Adam Lanza was able to kill so many Sandy Hook Elementary School students and teachers so quickly more than two years ago was the weapon he used: A Bushmaster Model XM15-E2S semiautomatic rifle.

It is descended from weapons designed for the battlefield, and it performed like it. The assault lasted about five minutes. Police recovered 154 bullet casings discharged from the Bushmaster, fired loosely at a pace of one shot every two seconds.

Among the many outrageous aspects of that tragedy was the firepower of the weapon, which had been bought legally by his mother, Lanza’s first murder victim (the Connecticut state attorney’s final report is here). Now lawyers for the families of some of the victims are pursuing a lawsuit against the gun manufacturer, distributor and gun shop involved in making and selling the weapon Lanza used.

The legal argument has an uphill climb. In 2005, Congress adopted the Protection of Lawful Commerce in Arms Act, a shield law designed to protect makers and sellers of firearms from liability lawsuits. At the time, the gun industry was facing legal challenges by murder victims’ survivors and municipalities trying to force some accountability from those profiting by the millions of guns made and sold in the U.S.


The liability shield isn’t absolute, though. It does not protect the gun industry from lawsuits alleging “negligent entrustment or negligence,” leaving a door open to go after someone who sells a gun “for use by another person when the seller knows, or reasonably should know, the person to whom the product is supplied is likely to, and does, use the product in a manner involving unreasonable risk of physical injury to the person or others.”

The lawsuit, filed by the Koskoff Koskoff and Bieder firm in Bridgeport, Conn., alleges that the makers and dealers who handled that particular weapon reasonably should have known it would be used to kill a large number of people because that is exactly what the gun is designed to do. It’s a politically attractive argument for backers of gun control laws, but it’s hard to see the courts finding liability here based on “negligent entrustment” because there is nothing negligent in the legal sale of a gun. And the killer was not the person who bought the weapon, but her son, a step removed from what a gun seller could reasonably expect.

Still, I wish them luck.

The strongest part of the lawsuit, though, might be the case it makes that such AR-15-style weapons should not be sold to civilians. The lawsuit argues that Bushmaster advertised the gun as a military weapon for civilian hands, with phrases such as “the ultimate combat weapons system,” “the uncompromising choice when you demand a rifle as mission-adaptable as you are,” and this: “Forces of opposition, bow down: You are single-handedly outnumbered.”


That’s selling combat, not self-defense, and it makes a good case for banning civilian possession of such weapons. But that ship has already sailed: The gun lobby has been very effective at heading off efforts to revive an expired assault weapon ban. That political equation isn’t likely to change in the foreseeable future.

There has been some uncertainty over whether the previous assault gun ban drove down the nation’s rate of gun violence, especially since the vast majority of gun deaths involve handguns. Regardless, it’s hard to see a future Adam Lanza -- and there will be more -- being as lethally effective without access to these combat weapons.

Follow Scott Martelle on Twitter @smartelle