I would like to add to the comments that nancygrace made. If the person who murdered your sister, you also need to take precautions for you own safety. I would also agree that you need to talk to a therapist or even your pastor to work through you feelings.
Please see a social worker or a counselor.You need to be able to talk about this horrible incident in a safe environment. Also, see a physician who can help you with medication to help you relax and sleep.
Also get help and support from you church and your friends. Experiences like these call for a lot of support for the difficult feelings that you are bound to experience.
Concentrate on taking care of yourself with expert and other help. Let us know how you are later, or write us here. It is very healthy to write about difficult experiences.
The best to you.