How Do You Forgive A Murderer?

My mind was going on and on. People would be talking to me and I would be looking them right in face and not hearing a word they was saying. My mind was on Kenny, and the person who shot him. Why? How could you shot someone and go home and go to sleep. How could you? I asked myself over and over again. I couldn't get an answer and to this day I still don't understand. Does it take understanding to forgive?