Clifford Olson

Clifford Robert Olson Jr. (January 1, 1940 – September 30, 2011) was a convicted Canadian serial killer who confessed to murdering 11 children and young adults between the ages of 9 and 18 years in the early 1980s.^[1] 

Olson is shown to be mentally ill, as evident by the fact he scored 38/40 on the Psychopathy Checklist.