I know some theory about Karma. As per my understanding, the fruits whether good are bad that we experience in this life are the results of the past lives.
Having said that, If somebody got murdered even if he is an innocent person and done no harm to anyone in this life, how to know whether this is a cause or effect? i.e. Is the murdered done some bad in his past life OR the murderer will experience the effects of this incident in his next life. Is it the beginning or the ending of Karma?
What you’re asking is, “Do unpleasant things ever happen to us without our having caused them, with the result that our karmic bank account shows a positive balance?” I suspect we all would like it to be true, so that when unpleasantness happens to us, the blow would be softened by the knowledge of a balancing pleasant event in the future.
But the simple answer is no: Everything that happens to us — pleasant or unpleasant — is the result of our past actions. In your example, the murder victim will have done something in the past (this life or a previous life) that has brought this upon him/her in this life. And the murderer will have to suffer the consequences of his/her crime, either in this life or a future life. So the event is the completion (partial or full) of a karma for the victim, and the beginning of a karma for the criminal.
This is a simple answer, because karma is a highly complex issue. For example, some people who die in accidents don’t necessarily have the karma to die; rather, they don’t have strong enough karma to live, and their karma to live gets overwhelmed by others’ karma to die in that accident.