I think you would find a correlation between the rise of mass shootings and the rise of 24 hour national news saturation. There have always been mass killings but prior to the news saturation it took a pretty major event to grab national headlines. (I’m watching the news about a guy holding his wife and kid hostage in California and that’s not really worthy of national coverage)
I also agree that news saturation is probably a major factor in driving marginal people over the line along with a myriad of other societal factors.
I think you would find a correlation between the rise of mass shootings and the rise of 24 hour national news saturation.
...and even if you don’t who gets off listening to the manure that passes as “news” for hours on end. Only a crazy person IMHO. It is why all of them had to go to interim programming with something besides “news” or no news at all ala PMSNBC.