WASHINGTON (AP) -- The Supreme Court declined on Monday to hear a challenge to a state ban on assault weapons, semiautomatic rifles that are popular among gun owners and have also been used in multiple mass shootings.

The justices turned down a case against a Maryland law passed after the 2012 shooting at Sandy Hook Elementary School in Connecticut that killed 20 children and six adults. The shooter was armed with an AR-15, one of the firearms commonly referred to as an assault weapon.

Three conservative justices, however, publicly noted that they would have taken the case, and a fourth said he is skeptical that such bans are constitutional, indicating the court could soon take another look at the issue.

Several states have similar measures, and Congressional Democrats have also supported the concept. The challengers had argued that people have a constitutional right to own the firearms like the AR-15.

The case comes two years after the high court handed down a landmark ruling that expanded Second Amendment rights and spawned challenges to firearm laws around the country.

Ten states and the District of Columbia have similar laws, covering major cities like New York and Los Angeles. Congress allowed a national assault weapons ban to expire in 2004.

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