The official definition of a serial killer is someone who kills three or more people. But do they have more in common than just a statistic? The series looks deeply into contemporary serial killers, to the most meticulous killer of modern times, Sacramento's Dorothea Puente, the owner of the 'House of Horrors'. Then there are the educated killers, like Dr Harold Shipman, who is thought to have killed nearly 300 people who were his patients and Ted Kaczynski, the Unabomber, who held a PhD in Mathematics. At the other end of the scale, Los Angeles serial killer Lonnie Franklin was organised but not smart, his reign of murder led to the deaths of so many disadvantaged women.