I was not opposed to the assault weapons ban, but I don't think that will solve anything now. There are so many assault weapons out there, if you outlawed them you would just be creating a black market and drive up their price. Those that really want to get their hands on them will, just as they do with drugs today.
I still maintain that there is nothing that could have been done to stop this particular guy. If he didn't have access to guns, he likely would have built homemade bombs or something else in order to kill multiple people. This type of incident is rare, and sadly there isn't much that can be done to stop it.
If you want to stop the majority of gun violence, then I think you are more likely to succeed if you tackle the societal issues that cause everyday gun violence. One of the biggest causes of crime in this country is poverty. We have fought wars on drugs and terror, but we have abandoned the war on poverty, which is possibly the most important battle we face.