We might be able to do better. But ultimately we have to resign ourselves to the notion that it is fundamentally impossible to prevent all violent crime, even events such as these. This is true whether or not we could magically completely eliminate all guns on Earth.
Ultimately it's impossible to be knowledgeable of the bad intentions of every single warped individual on the planet. And some of those folks will have the capability of harming people, perhaps many people. Look at 9/11 as an example of how a handful of well trained and highly motivated individuals armed with only box cutters were able to take control of jumbo jets and ram them into buildings and kill thousands. That's an extreme example but it's worth remembering, because there are many, many examples of similar situations. Look at the unabomber, for example. A brilliant loner who was able to fashion bombs from household materials in a shack in the middle of nowhere and kill several people. Or look at all of the other bombers throughout history. You can't legislate away the ability to build bombs, they're already illegal, but anyone with enough knowledge and a little money can make them and kill people. The same goes for arson, which kills hundreds of people every year.
In my view the solution is not to try to disempower the entire populace by taking away guns and hoping that this disempowers the bad guys enough to make it that much harder for them to kill. I think that the better solution is to empower responsible individuals to act in their own self-defense and in the defense of others. I think it's also worth concentrating on social and cultural changes which make our society more accepting and hopefully make the creation of these violent individuals less common, but that's a much harder problem to tackle.