A Connecticut court has ruled that families of schoolchildren killed in the mass shooting of Sandy Hook in 2012 can sue US weapon maker Remington.
In a 5-4 vote, the US Supreme Court said that the lawsuit against US federal court could continue to be based on state consumer protection laws.
The weapon was used by Adam Lanza, who killed 27 people, including 20 elementary students.
The verdict is a rare legal defeat for an armaments company in a mass shootout.
The lawsuit of relatives of nine victims and one survivor points to the "militaristic" commercialization of Remington's AR-15 rifle. "The goal of the families has always been to illuminate Remingtel's calculated and profit-oriented strategy to expand the market for AR-15 and high-risk users, all at the expense of American safety," said Josh Koshoff's family lawyer Victim.
"Today's decision is a crucial step in achieving this goal."
Remington did not immediately respond to a request from the BBC for an opinion.
The proceedings were initially postponed after the company had filed for bankruptcy last year after the slump in sales.
An initial lawsuit against Remington was dismissed in 2016, and the families were brought before the highest court in the state last year. It is expected to go to the US Supreme Court.
Under US law, weapons manufacturers and dealers are legally shielded from legal liability if their weapons are used in criminal activities. Exceptions apply in case of harmful marketing.
"It seemed unbelievable that this industry would enjoy such protection," said David Wheeler, father of a Sandy Hook victim, in an interview with The Financial Times.
"It's hard not to look at this [ruling] and think that states may be swinging in a more rational place."
A wave of shootings in recent years has sharply focused the debate over American gun laws moved the focus.
Some US retailers have responded by raising the age limit for certain firearm purchases to 21 or stopping the supply of semi-automatic weapons.
Last month, the country's House of Representatives approved a bill that expanded the background checks on all arms sales.
Critics of the legislation say the changes have not stopped many recent shootings, and President Trump has pledged to veto the bill if it denies the US Senate.
Lanza killed 20 students and six employees at the school. He had shot his mother before. When the police approached the school, he killed himself.