If you killed someone in a dream, then it means that you have much of anger hidden in your mind. You have problems while dealing with all of the stress, therefore you are willing to kill someone. You lost the control of yourself. If you witness killing, then it means you are not very happy about the variations that happening around you. If you dream of killing the wild animal, you will reach your success.
Read more about dreaming of Killing in other dream meanings interpretations.