Dreams communicate through symbols and metaphors, so "killing" in a dream often represents something quite different. Dreams can use literal pictures as we will use words: for example, the common phrase, "You're killing me," actually means, "You are making me laugh too much." So look at other details of the dream for clues as to its meaning. Also, see the attached link for more info on dreams and their symbols.
you just either saw a scary movie or it was a random thought
If the dreamer actually killed someone in real life, then dreams about that person, the dream suggests feelings of guilt and remorse. If the dreamer only dreams of killing someone, the dream suggests anger with that person.
that you are a cat person
You once felt a guilty feelings to that someone you mentioned...
Dreams are about the person having the dream. So this other person's dream is about that person, not you.
The question cannot be answered without further information; a dream about killing domestic animals for food or killing dangerous predators would be very different from a dream about the cruel killing of pets, or senselessly shooting harmless wildlife.
The "someone" in this dream might represent the dreamer's own self. The "killing" is a metaphor illustrating the dreamer's anger or disappointment with one's self.
This dream suggests that some part of your self really does not approve of that person.
Freud said "Sometimes a cigar is just a cigar." This means sometimes dreams are simply what they are and have no meaning.More information:Both the person being killed in your dream and the action of killing are symbols pointing toward something else. It does not mean you would not feel terrible actually killing someone. If the person you killed is a stranger, the dream takes on a slightly different meaning than if your victim was someone you know. Stranger = the act of killing is the focus. Known person = that person or what they represent is the focus. ... The absence of feeling might suggest that the "killing" is impersonal, in the sense of "it's just my job." So the dream might be telling you that something you are doing because of your work or your position, etc., places you at a false sense of distance from the consequences. Just because you do not feel the affect of your action does not make those affects less real.
This dream only means that the person interests you. Your mind might be using the image of this person to represent something in your dream, such as an attractive, exciting person, or, contrarily, a scary, threatening person. In any case, your dream does not mean that the person was thinking or dreaming about you.
This dream suggests a fear that a part of the self is being silenced. The murdered person represents some part of the dreamer's self that is being denied expression.
This dream suggests that you are "sick with grief" over the loss of this person.
This suggests that the dreamer is coming to accept the reality of that person's death.