How do I speed up the mourning after a murder and why am I so upset?!?

This is survivor's guilt. You think it should have been you, you should have been there with them to prevent the murder. Try to look objectively at the situation - you had no way of knowing this would happen. The girls chose a risky way to travel, also chose to travel home without you. You couldn't have stopped them from making their own choices. Your response reflects that you're a sensitive guy with a higher than usual sense of responsibility to people around you. You need to see your GP to help you cope with these emotions. Am hoping for your speedy recovery, sending you lots of best wishes.