They did, if even indirectly. Just like how McDonald's holds some responsibility for the obesity epidemic.
The company that makes rifles makes them to be sold. It is in the company's best interest that as many mass shootings happen as possible. By providing guns, they DID contribute to the tragedy. We can tell, because if they had never produced that gun then it would've never shot anyone.
This doesn't even touch on the fact that the reason gun laws are so lax is because these companies lobby for it to be so. Again, they are incentivized to cause as many people to die as possible. Incentives matter. If mass shootings were the next blue jeans, these companies would quickly overthrow Apple.
Blame is very hard and tricky, but any institution or system in place is responsible for an intuitional failure. And that's what mass shootings are - an institutional failure.
They didn’t though. Holding a rifle manufacturer liable for a shooting makes no sense, unless applied universally.
A journalist writing a book did not cause the shooting.
This is greed and lashing out in pain. I’m sure members of the community have ruined their life in pursuit of these things.