I read the article, and chose my language accordingly (“had been on a terrorist watch list”). My biggest concern isn’t ‘what if X regulation would have prevented the Y shooting’, as much as how shitty it is that our congress has been unable to consider any sort of firearm based legislation to address the problem, no matter how large of a majority of voters support it. People have been led to believe that the second amendment forbids any firearm regulations that we don’t already have, and that’s simply not true.
I’m also not sure how you can say that the assault weapons ban did zero to prevent or reduce the casualties from mass shootings. The deadliest shooting from '94-’04 was Columbine (13 dead), but since 2004 there have been six deadlier shootings, three of them using assault weapons. I think it’s fair to argue that Columbine could have been worse if they had AR-15s. On a side note, the columbine shooters used a legally purchased Uzi-type gun (arguably the best gun legally available at that time to kill people fast) that I think should probably also be restricted. Then you have a situation like the Aurora theater shooting, where over 50 people were wounded and 12 killed. I think it’s fair to assume that without the assault rifle he probably wouldn’t have been able to shoot that many people so quickly.
Like you said earlier, most people have their minds made up, so I’m not sure the statistics are worth much anyway. Even if it were absolutely undeniable that an assault weapons ban would help, opponents of it wouldn’t change their minds.