Velma Margie Barfield
Barfield had poisoned four to seven people including her mother, her employer,
and several husbands or lovers -- most so they would not find out that she had
stolen money from them to buy drugs.
http://www.geocities.com/trctl11/barfield.html
http://www.fayettevilleobserver.com/news/archives/1998/tx98feb/n4cheek.htm
Book: "Death Sentence: The True Story of Velma Barfield's Life, Crimes and Execution"
(autobiographical): http://hallmemoirs.com/specific_groups/165.shtml