That's the same question people always ask of god. Why, if he is so good must there be so much suffering in the world.
There is no justice in the world. Because god is not good or bad.
Karma creates suffering, Living is suffering.
You can't blame karma for killing these people, we all know who killed this people. If you kill people (for example) you create suffering, this is karma.
The way to end this suffering is said to be karma yoga.
Let me say that I don't use the word karma often. I dislike it, because of the stuff you point out.
I just wanted to make clear my understanding of this concept. I don't believe in reincarnation, and stuff like that.
I believe there is a lot in the concept of karma that putts people down.