The US Supreme Court has refused to protect a major firearms manufacturer from potential liability in the 2012 shooting at Sandy Hook Elementary School, paving the way for grieving parents to try to hold the company accountable over its alleged part in the massacre that left 26 students and staff dead.

The decision by America's highest court will allow families of victims of the shooting in Newtown, Connecticut, seven years ago to move forward with their allegations that Remington Arms Co had marketed the military-style rifle used in the attack "for use in assaults against human beings".

The lawsuit, which will move forward at the state level, will test a 2005 US law favoured by the National Rifle Association (NRA) that aims to protect gunmakers from being held liable for crimes committed by the people who buy their weapons.

The Supreme Court's decision upholds an earlier Connecticut Supreme Court ruling in March, which determined that Remington can be sued for the way in which it marketed the AR-15-style Bushmaster rifle, which was used in the shooting. Families contend that Remington glorified the weapon in advertising that targeted young people, including in video games.

Gun-control advocates say that a legal victory against Remington would likely be only the beginning of lawsuits against the firearms industry, which counts the among its friends in Washington and across the country the powerful NRA – a successful champion of pro-Second Amendment laws in legislatures across the country.

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If the Sandy Hook families win, advocates say, the victory will almost certainly be followed by further lawsuits and damaging disclosures about the way in which the firearm industry markets and sells its products.

The shooting at Sandy Hook Elementary School in 2012 was one of the most shocking mass killings in American history, and led to widespread calls for gun-control reforms as the stories of children getting gunned down at school spread in its wake.

The shooter, 20-year-old Adam Lanza, had killed his mother at home before going to the school, where he killed first-graders and staff and then turned the gun on himself.

The Supreme Court is also set to hear arguments in December on a separate gun-rights case, stemming from a New York City regulation that would restrict the transportation of legally owned guns, which owners say violates their constitutional rights.

Donald Verrilli, the lawyer representing the families suing Remington, said in court papers that the company's advertising "continued to exploit the fantasy of an all-conquering lone gunman, proclaiming: 'Forces of opposition, bow down. You are single-handedly outnumbered.'"