As well as"The Alchemist" which jenisedai recommended, another book that you might like is "The Poisoner's Handbook: Murder and the Birth of Forensic Medicine in Jazz Age New York" by Deborah Blum (2010). It is a great book, and it does deal with specific poisoning crimes from that era, the techniques used to investigate the cases, and the early evolution of forensic medicine.
I am talking about war... and I am also talking about gaining something. People kill to gain something in a world built on gaining... rather than one built on sharing. In a sharing world there is less reason to kill. Given some people are crazy. But this is like 1 in 1,000,000. Probable even lower than that. Point is most people only turn to killing because they want to profit some how.
You know what would have avoided that womens death... not needing money to live. How many people murder just to gain some kind of wealth. How many killers do you know who wasn't after money, or trying to protect something. Think about that.