This was decided before, on October of 2016, in Connecticutt. It was pretty well laid out in a 54-page decision. It's gonna get overturned, and it looks like a politically motivated decision this time...
https://www.pbs.org/newshour/nation/judge-tosses-sandy-hook-lawsuit-gun-maker
In 2005, the Protection of Lawful Commerce in Arms Act was passed, asa United States Law - and is the result of the DC Sniper rampage that those two idiots did. Here's what it is:
"The Protection of Lawful Commerce in Arms Act (PLCAA) is a United States law which protects firearms manufacturers and dealers from being held liable when crimes have been committed with their products. However, both manufacturers and dealers can still be held liable for damages resulting from defective products, breach of contract, criminal misconduct, and other actions for which they are directly responsible in much the same manner that any U.S.-based manufacturer of consumer products is held responsible. They may also be held liable for negligent entrustment when they have reason to know a gun is intended for use in a crime.
The PLCAA is codified at 15 U.S.C. §§ 7901-7903."
So, there's the law protecting the Arms Manufacturers. Gonna be pretty hard to "prove beyond a reasonable doubt" that Bushmaster/Remington, as a company, KNEW what that little fucker planned to do with that rifle - in the future, after the point of purchase... This is gonna get squashed.