Sandy Hook Families Take Fight to Gun Maker: 'We're Never Going to Move On'

— -- The family of Victoria Soto, the first-grade teacher who was fatally shot at Sandy Hook Elementary School as she tried to shield her students, said today they'd joined a lawsuit against the maker of the Bushmaster AR-15 that killed Soto and 25 others to honor the sister they described as "amazing" and like a "second mom."

"We're never going to move on," Jillian Soto said. "My sister got married and [Victoria Soto] wasn't there for her wedding. I'll graduate in a year from school and my sister won't be there. ... You don't move on from your sister being brutally murdered in her first-grade classroom. ... We live every day with the pain that our sister's gone."

On Dec. 14, 2012, Adam Lanza, 20, killed his mother before storming into the Newtown, Connecticut, school and killing 20 children and six adult school employees. Five of the 16 kids in Soto's class were slain.

The families of 10 victims filed the lawsuit Friday against the maker, distributor and seller of the rifle. In addition to Bushmaster, the families named Camfour, a firearm distributor, and Riverview Gun Sales, the store where the Bushmaster rifle was purchased in 2010. The lawsuit alleges negligence and wrongful death.

"I can't say if my sister would be alive if Adam [Lanza] walked in with other types of guns because no one knows what could have happened but Adam walked in with that gun that day, into my sister's classroom and killed my sister along with 25 other people," Jillian Soto told ABC News.

Carlos Soto, who was 12 years Victoria's junior, said that the families had gone to Washington and lobbied, speaking with senators and representatives to effect change on the federal level, but nothing had come of their efforts. In April 2013, the Senate failed, 54-46, to pass a key gun control measure that would have expanded background checks for people buying guns online and at gun shows.

The Sotos said the families had decided that the next best route would be going after the maker of the gun and the people who had sold it.

"I hope to get the gun industry to accept responsibility," Jillian Soto said.

Bushmaster did not respond to ABC News requests for comment.

Under federal law, however, gun manufacturers have blanket civil immunity from liability resulting from the criminal or unlawful misuse of their weapons. This applies in federal and state courts.

The 2005 law, the Protection of Lawful Commerce in Arms Act, effectively shields manufacturers and dealers when someone uses a gun in commission of a crime. There are some exceptions in the law.

One of the exceptions is for "negligent entrustment," which allows lawsuits to proceed if it can be shown that a seller was negligent in allowing a person to possess a gun "when the seller knows, or reasonably should know" the person is likely to (and, in fact, does) use the gun to harm himself or others.

The Newtown families are asking a state judge to broadly apply that negligent entrustment exception.

They are not alleging negligence against the seller for specifically allowing Lanza to possess the weapon -- it was purchased legally by his mother -- but rather that all the defendants are negligent for marketing and selling what is essentially a military weapon for civilian use, and for entrusting any civilian to possess one.