Rampage:

Rampage: the Bloodlands series by: Harold Schechter
Non-fiction: History, E-book
E-book Count:22
Book Count:31

This book is the story of Howard Unruh who killed 13 people on September 6th, 1949.  He is known as "The Father of Modern Mass Murder" because of this.   Unlike many people who kill in a spree like this he didn't kill himself at the end of his spree, nor did he commit suicide by police.  So there are records of him recounting the details of his crimes.  There was also the issue of determining if he was legally sane.  He was very a matter of fact and unemotional of his crimes, causing people to argue about whether he should stand or be placed in a mental institution.  He ended up in a high security mental institution and so outlived most everyone involved in his case, dying in 2009.  (Rather then being executed, like would have happened if he was tried in the murders.)