This horrible attack came unexpected, so I would include it in the list of words, the word “tragedy”.
Well, I do not concur on the use of the word tragedy to refer to an attack by the very nature of it being intentional. For some it may have been a surprise, but not for all. From the view of an individual personally injured it can be tragic experience, but not so much with the event itself.
I like to make a clear differentiation between horrible events occuring without intent and horrible events occuring with intent. We have so many words that allow us to do just that.