11/07/2011 09:38 am ET Updated Mar 02, 2012

10 Horrifying Serial Killers

A serial killer is defined as someone who kills three or more people over a long period of time.

They are usually male and possess a "mask of sanity," which means that on the surface, they appear to be normal law-abiding citizens with a pleasant demeanor.

However, beneath their facade serial killers are sociopaths who lack the capability to empathize with the suffering of their victims.