The person who kills someone in the dream is experiencing some pressures subconsciously or this is the manifestation of the violence in the inner world of the dreamer. In some cases, this dream is a psychological condition that happens to most people, influenced by a movie you watch or an event you hear. Those who witness scenes of violence in a movie they watch often see something like this in their dreams.
It is a symbol of despair. It expresses that the person feels very vulnerable psychologically, has a thought like helplessness from time to time, and has difficulty in continuing his daily life. It also symbolizes that people who try to forget their problems by giving themselves to work, engage in different activities in order to improve their moral motivation.