How mean can this world be?

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This is regarding an incident that took place in India in the year 99. A group of people stormed into a class room and killed a teacher while he was teaching his students. He was stabbed and murdered using a sword in front of those small kids. It took months for those children to recover from that shock and that too only after many counseling. The court verdict was not to punish those who were involved in this case due to inadequate evidence. When i read this i was shocked and just thinking how mean this world is? After killing a person in front of many small children all those who were convicted were released without giving any punishment. Isn't this a License to Kill anyone? What is the use of a judiciary then?