a classmate
It was many moons ago when I was a first-year student at a high school, and there was a so naive guy who used to joke, socialize and share his personal info. I was learning basic human anatomy and killing methods as well as I was working on my own emotions. Once, I wanted to examine what I was capable of, then I leaned about him deeply. After half a month of learning and planning, I have decided to kill him without any traces, witnesses and etc. He was having fun with a few friends along the sea. I went there and kidnapped him without making any noise and brought him a shit hole where no one is every interested in. Eventually, I killed him like a maniac, and got rid of his body by using some chemicals and burying.
The results:
No one even suspected me, and every one thinks he drowned that day.
Mentally, I have not felt any emotions because of that.