Judges on the Connecticut Supreme Court heard arguments from lawyers representing the families, gun manufacturer Remington, the Connecticut shop that sold the weapon to the shooter's mother and Massachusetts-based arms distributor Camfour.
The state Supreme Court will decide whether the case is valid enough to go to trial. He said the Bushmaster rifle and other AR-15-style firearms were designed as military killing machines and are too unsafe for the public, but Remington glorified them and marketed them to a younger demographic that included the 20-year-old Lanza.
Families of nine victims who were killed and a teacher who survived the December 14, 2012, massacre filed the lawsuit in January 2015 seeking to hold Remington liable, arguing it marketed the AR-15 to the public even though it knew the weapon was designed for military use.
"What happened in the school that morning was horrific", Vogts said.
Plaintiffs' attorney Josh Koskoff said the families want the high court to return the case back to the Bridgeport Superior Court so "the discovery phase of this case can begin and we can start uncovering documents on how this military weapon ended up in civilian hands".
"In the military, a weapon of this type is quite rightly subject to strict rules around its use and storage", Ian Hockley, the parent of a Sandy Hook victim, said after the hearing.
The packed courtroom in Hartford, Connecticut, included numerous victims' family members.
Judges have cited the federal law in rejecting lawsuits against gun makers and dealers in some high-profile shooting attacks, including the Colorado movie theatre shooting and the Washington, D.C., sniper shootings.
"But we have not lost one ounce of confidence in the validity of our case", he said.
"Make people interested in buying your products and I would point out that the advertisements the counsel has referenced were not necessarily directed to a younger demographic", Vogts said.
Legal experts said the case comes down to how the state Supreme Court will interpret two possible exceptions allowed under PLCAA - whether Remington can be held liable for so-called "negligent entrustment" or whether it violated the Connecticut Unfair Trade Practices Act. Negligent entrustment is specifically excepted from the 2005 gun maker shield laws. Lanza also killed his mother before the school shooting.
The argument has historically been used where someone lends a vehicle to a high-risk driver who goes on to cause an accident. "Under the law. the manufacturer and the sellers of the firearm used by the criminal that day are not legally responsible for his crimes and the harm that he caused".
"What we have here is the conduct of a corporation that thought it was above the law and still thinks its above the law", said lawyer Joshua Koskoff.