The Killer Confession

A serial killer who got caught after many years of murdering many people. Finally after being locked behind bars for serving time for the crimes he has committed. He decides to come clean about the murders that he has committed. Murdering innocent people, he now allows all the family to grieve knowing he is in jail. Then soon to know why he did all of this. Days before he is put to death in jail. His last wish was to be able to write in a composition book his whole life and the reasoning why he kidnapped and killed those people. So people will no longer have to wonder why. Will you be able to guess the reasoning why he did what he did before he is strapped to the chair and put to death?