"If only someone had a gun then they could have shot him"
Forgetting that he would have then likely had a gun himself and we end up at the exact same situation in the US with Mass Shootings happening so regularly it doesn't even make national news.
Kinda goes to prove the point that all these killings aren't a gun issue since mass killing is possible either way (its just easier with a gun). Taking guns away would be akin to placing society in a giant old school mental asylum where we are all in straight jackets. Sure we would all be killing each other a lot less when we are in straight jackets all day, but it doesn't stop the violent thoughts and ideation.
I know what alleged means. And in this context, it means they either shot the guy who was stabbing people or shot someone else, meaning they don't know if it is or isn't the guy they were looking for.