We now know enough about this guy - based on the numerous traps and bombs found in his apartment - to know that he could have just as easily have used one of his homemade bombs to do as much, if not more, injury and death.
The sad reality is that we are never 100% safe, especially when in a public venue. That's not a new reality, just one we're getting more first-hand knowledge about. Those intent on killing will find a method. Gun - bomb - airplane. There's always a way. Add security in one spot to try to stop it and they will look for a new weak spot and they'll find one.
Obviously, this guy is mentally ill but were there any signs? Were they ignored? He was collecting unemployment so where did he get the funds for all this? Why weren't his parents surprised when they learned what their son did? There are many questions yet to be answered.
Dealing with mental illness is the bigger issue. We need to know how to identify those that are a danger to themselves and to others and we need a legal means of making sure they get treatment.