Not being able to wrap your mind around such a horrible event is a good thing. The only people who really need to try to understand such things are those who's job it is to try to prevent them.

And those people pay a heavy psychological toll for trying to understand such horrors.

You have a good heart, mourn for the victims and their families, and try (I know it's hard) to put the evil doers out of you mind, they want to be remembered try not to grant them their twisted request.