It is easy to misinterpret a dream where a person or people die somehow. You might die, you might be doing the killing, or as in your dream you witness someone else kill someone, or in this case a number of people.  Try to remember, that the dream weaver part of you is not viewing death from the same perspective.  In their view, there really is no death.  Death is symbolic of something else, as most things or events are in dreams.  Death usually represents a major change taking place in the live of those who are dying. It means the end of the old and beginning of a new direction in life. In real life, the "killer" might be a teacher or spiritual leader of some sort who has a profound effect in certain people's lives. He helps them to see their greater potential, leading them to make life-changing choices.

 The party represents a social group of people whose main concern is living superficially, irresponsibly, a group you may be being drawn to, Doing so would take you away from what you desire most.  Just as fear in your waking life is your emotional guidance system telling you to rethink the direction your heading in or the choice you are about to make.  On the other hand, sex, which likely represents pleasure and symbolizes a decision more conducive to you true desire. Should tell you something. Ultimately you must determine the meaning of your dream symbols for what they mean to you. This is only one interpretation.

  The guy could also represent someone your interested in relating more closely with.  He may seem to be the ideal guy, charming in every way, until he gets what he wants then dumps you soon after, as revealed by the act of killing. A broken heart can often seem like a fate worse than death, and does on occasion lead the heartbroken to actually kill themselves due to the emotional trauma. If that were the case then you might be lying to yourself, getting into a relationship where " you knew his secret all along".

   It could be a positive thing; in that you may be the one who cures him of his womanizing ways, you are the one he can connect with on a deeper level.  In that case, the dream might be telling you to go ahead and risk it. Don't be afraid to take a chance on love again. Have you ever used the word "killer" as an adjective describing something or someone as super cool, top of the line etc?  A real dream interpretive reading involves a lot of questions by the interpreter. These questions are not asked with the expectation of an answer. They are asked to assist the dreamer to recognize the meaning of the dream. Dream reading sessions often end abruptly when the dream suddenly has an "aha" moment when all the pieces come together with what's currently going on in the dreamers waking life.

  Hope this helps you find the right meaning to your dream. The key thing to remember is that YOU are the writer, director, producer and lead actor in your own late night play, although "symbolic soap" might be a better description:)