1. First of all, Kamma is one of those things that the Buddha categorized as “acinteyya”, not fully graspable by a human other than a Buddha.
2. There are two key factors to be remembered in evaluating how to assess a kamma vipaka:
–which of the dasa akusala is the intention? That is the “cetana” in “cetana ham bhikkhave kamman vadami”.
– then the strength of the kamma vipaka is based on the “level of consciousness” or “qualities” of the living beings affected by that kamma.
-That is the clearest way to analyze any given situation.
3. For example, in the recent second desana on Tilakkhana, I discussed the case of a person killing a bunch of people with a bomb. His intention (cetana) was to kill. Thus the dasa akusala involved is “panatipata”, that of taking a life.
-Now to the second step. He may not even know who was killed. By some coincidence if a parent of the killer was killed by the bomb, then he would have done an anantariya papa kamma. If an Arahant was killed, the same. If a Sotapanna was killed, then it would not be a anantariya kamma, but still equivalent to killing thousands of normal humans.
-So, it is important to understand that “cetana” is which of dasa sakusala are in one’s mind when a kamma is committed. It could be more than one. In the case of the bomber, there is micca ditthi, and likely greed also, in addition to “panatipata”.
-So, it is good to analyze various situations with the above two steps.
4. In the particular example discussed, it is not necessary that person A had to have killed B in a previous life. It is just that person A had a previous kamma vipaka waiting to bear fruit and he himself made the conditions right by going to a bad neighborhood, possibly at a bad time.
Person B could have been just happened to be there with the appropriate mindset to do the killing. It is also possible that there could have been some connection between the two in the past, but that is not necessary.
We all have done innumerable kamma in the deep past and when suitable conditions appear they are brought to fruition.
-But there are some accounts in the Tipitaka, where a person “avenges” a previous death by killing. But in those cases, person A would have killed person B in a previous life by beating him, for example. Then person B would have made a determination, “I will kill you in the future in return”.
-But if person B in the given case kills A by shooting from a distance, A would even not know who killed him. He may die instantly, not even being aware that he was shot by someone. Of course, the “nature” would know (we are all connected), and therefore, that could act as an additional factor.
– This point of “we are all inter-connected” is now proven by quantum mechanics: “Quantum Entanglement – We Are All Connected“.
– This is a key factor in understanding kamma/vipaka, and is my next project. I believe that quantum mechanics can show this at an even deeper level.