I strongly suspect that the suit against the gun companies will be thrown out. They complied with the laws, and the guns functioned as firearms are intended to function. The PLCAA was written precisely to prevent this kind of bad-faith lawsuit, where a company is being held responsible for the illegal used of their product. Imagine how batshit crazy it would be if you sued a Ford dealership for selling a car to someone that had a secret drinking problem, and that person then drove drunk and killed a bus full of schoolkids. What magic divination is the gun store supposed to use to figure out that a person is a mass-murder-to-be, and how do you ensure that no people that aren’t going to be mass murderers aren’t being denied their constitutional rights? Now, if the shooter was buying guns and armor, and told people, hey, what gun is going to be best for killing people in a supermarket?, then yeah, they have a case for negligence. But I’ve got an AR-15, and I’m working on saving up for body armor, because I need both for the kind of shooting competitions I’m interested in. Given how many AR-15s there are–over 24M in civilian hands, or about 1 for every 13 people–and given how many people own some form of body armor, compared to the number of these random, mass-murder events there are, neither purchase would normally raise any suspicion.

The case against the social media companies will be a challenge, because that’s going to largely be covered by 1A issues, unless they can point to issues that amount to incitement.

Parents are a stretch as well. They’d likely have to have some kind of finding of gross negligence in order to hold them responsible.

If you really, truly, deeply care about preventing this kind of tragedy, then you need to start addressing root causes of this. The FBI published a report a year or two back about profiling this type of murderer, and it turns out that it’s really hard because they’re so very rare.