Don't Feel Bad When I Die - Don't feel bad when I die, #1

The story follows a boy visiting his former teacher after 4 years, gives her a present(a story) that he says he has written by himself and she is in it somewhere. As the teacher reads the story she finds the story includes murder that the boy had committed. How he does that? What are his motives? Does he get caught? And most importantly how the teacher fits in all of this?  If you want the answers read it and find for yourselves.(Note:- The first part of the story focuses on how he commits the murder and the challenges he faces while doing it.
The second part focuses on the investigation and the third(last) part focuses on the conclusion of how he gets caught or how he gets away with it?