4. Harold Shipman
Harold Shipman, also known as Dr. Death, worked in health offices in London for a long period of time, and took advantage of his profession to to kill a large amount of his patients (218 or even more). He was never caught until 1998, when another doctor discovered that Harold Shipman had put his signature on an enormous number of cremation certificates.
These documents gave the first clues that Harold used to commit murders at his workplace. When inspecting the victims of the doctor, it was revealed that most of them were women.
Shipman’s effort to fake a will and add himself as a recipient of a dead mother was uncovered by the daughter of his last victim. Shipman used fatal quantities of diamorphine to murder his victims, according to an autopsy. Shipman was imprisoned in 2000 and committed suicide in 2004.