The families of nine victims that were shot dead in the 2012 Sandy Hook Elementary School massacre have filed a lawsuit against manufacturers of the gun used in the attack.
They said that the weapon should not have been sold because it had no reasonable civilian purpose.
While the AR-15 assault weapon used in the attack on Sandy Hook Elementary School was legally sold in Connecticut, the lawsuit contends that the weapon should not have been available to 20-year-old gunman Adam Lanza.
The AR-15 is manufactured by Bushmaster, a privately held company based in Windham, Maine.
Lanza shot dead 20 first-graders and six educators on 14 December 2012, which stands as one of the deadliest school shootings in US history.
The massacre sparked a fresh debate on gun rights, which are protected by the Second Amendment of the US Constitution.
"This is a weapon that is designed for military use, for killing as many people as efficiently as possible," said Michael Koskoff, a lawyer for the plaintiffs.
"It's negligent for any seller to sell a weapon like that to the general public."
The lawsuit, filed in Connecticut Superior Court in Bridgeport by the families of nine of the people killed in the attack and a tenth person who was wounded, seeks unspecified monetary damages.
The 40-page suit names Bushmaster as well as a weapons distributor and the retailer that sold the gun used in the shooting as defendants.
After the Sandy Hook shooting, Connecticut's Democratic governor Dannel Malloy pushed through one of the strictest gun laws in the United States, banning more than 100 types of military-style rifles and limiting ammunition magazines to ten bullets.
However, even as Connecticut and neighbouring states tightened gun rules, other states rejected new curbs on gun ownership.
Bill Sherlach, whose 56-year-old wife Mary Sherlach was a school psychologist killed in the attack, said the suit was necessary to hold gun makers accountable.
"I believe in the Second Amendment but I also believe that the gun industry should be brought to bear the same business risk that every other business assumes when it comes to producing, marketing, and selling a product," Mr Sherlach said in a statement.
Lanza, who began the shooting spree by killing his mother at their home, ended his rampage by turning his gun on himself a she heard police approaching.
