EDIT: I see my post is being downvoted. I know that it may come across as insensitive to immediately leap to the gun control debate, but frankly I'm more angry than upset by this news. How many times does it have to happen? We have a good 48 hours of emotional outpouring and then everyone forgets it ever happened.
Second mass shooting of the week. "Guns don't kill people, ..."? Please.
Things aren't the problem. People are the problem.
If you have to use a knife to kill someone, you are going to have to get very close to them to do it. You're going to have to be very aware of what you're doing. With a gun.. not so much.
Knives are simply much slower and less efficient for the task, especially against forewarned opponents (e.g. most of the potential victims in many mass-killing situations, and potential defenders), and it's vastly more likely the attacker will be stopped quickly even if he manages to kill a few people.