i understand this well because it happens to BP pts called mixed states quite often. Most probably your mood is low while you are plenty of energy and there lies the need to revenge and kill. Many of the crimes which occur in real life are due to mixed states
I found seroquel helpful in this regard, but other drugs also help. I advise you to consult a pdoc even though you haven't killed someone yet. Because the drugs will stop these compulsions which you feel without doing much effort on your part or to keeping questioning them on and off
Just because you have these thoughts doesn't mean you will kill someone; however, you should probably have a few therapy sessions to delve into why you have these thoughts idolizing killing the way you do. If you explore the topic with a therapist and figure out the reason, you will be able to begin to learn how to better overcome the thoughts, which would hopefully lessen the severity or occurrence of them and the likelihood of ever acting on them. Don't ignore the fact you're having these thoughts. It's a little concerning that you don't express fear of the thoughts so much as fear of going to jail, going to hell, or fear of guilt that accompanies the act should you ever were to choose to go through with them.
The fact you've posted here means you want help and you seem to genuinely not want to act on them, but now it's time to take the next step. You don't have to tell anyone you're even seeing a therapist or if you choose to do so, it's not necessary to tell them why. The therapist will help you learn what the cause is and figure out ways to deal with the thoughts and take control.