So if we were (for example) sure a person had committed rape, and had good evidence they also committed murder, it is up to the prosecutor to decide if they sho

So if we were (for example) sure a person had committed rape, and had good evidence they also committed murder, it is up to the prosecutor to decide if they should risk pursuing a murder charge, risking a person going free for a rape which they would certainly be convicted for? Also, if you do murder someone, you may as all rape them too, as it can't lead to any more sentence?