^A serial killer is most commonly defined as a person who kills three or more people for psychological gratification; reliable sources over the years agree.
R. Barri Flowers. The Dynamics of Murder: Kill or Be Killed. CRC Press. 2012: 195 [June 15, 2016]. ISBN 1439879745. (原始内容存档于2016-09-01). In general, most experts on serial murder require that a minimum of three murders be committed at different times and usually different places for a person to qualify as a serial killer.
Harold Schechter. The A to Z Encyclopedia of Serial Killers. Simon and Schuster. 2012: 73 [June 15, 2016]. ISBN 1439138850. (原始内容存档于2016-09-01). Most experts seem to agree, however, that to qualify as a serial killer, an individual has to slay a minimum of three unrelated victims.