Karma is complicated. Can you understand all the motives, thoughts, and desires driving you to act during a single event, situation, or ordeal?
Now imagine this event, which is compounded by so many factors and people. Is it even possible to simplify such a tragedy with one cause?
The truth is that you can find answers, but not in the physical plane. You have to awaken internally to understand the deeper causes of suffering of this type. Each situation is unique.
Gain a more complete understanding of karma by studying the following book:
For thirty years I sought God. But when I looked carefully I found that in reality God was the seeker and I the sought. -Bayazid al-Bastami