http://listcrown.com/top-10-brutal-serial-killers-ever/
http://homesecurity.net/serial-killers/
http://www.therichest.com/featured/top-10-most-notorious-serial-killers-of-all-time/
http://www.fearnet.com/news/list/worlds-most-prolific-serial-killers
http://www.mirror.co.uk/news/uk-news/10-chilling-serial-killers-and-how-814426
http://memolition.com/2014/03/08/top-ten-serial-killers/