Serial killers who worked in law enforcement

Dennis Andrew Nilsen (23 November 1945 – 12 May 2018) was a Scottish serial killer and necrophile who murdered at least twelve young men and boys between 1978 and 1983. Convicted at the Old Bailey of six counts of murder and two of attempted murder, Nilsen was sentenced to life imprisonment on 4 November 1983, with a recommendation that he serve a minimum of 25 years; this recommendation was later changed to a whole life tariff in December 1994. In his later years, Nilsen was imprisoned at HM Prison Full Sutton in the East Riding of Yorkshire.
All of Nilsen's murders were committed at the two North London addresses where he lived between 1978 and 1983. His victims would be lured to these addresses through deception and killed by strangulation, sometimes accompanied by drowning. Following each murder, Nilsen would perform a ritual in which he bathed and dressed the victim's body, which he retained for extended periods of time, before dissecting and disposing of the remains by burning them in a bonfire or flushing them down a toilet.
Nilsen became known as the Muswell Hill Murderer, as he committed his later murders in the Muswell Hill district of North London. He died at York Hospital on 12 May 2018 of a pulmonary embolism and a retroperitoneal haemorrhage, which occurred following surgery to repair an abdominal aortic aneurysm.

François Vérove (French pronunciation: [fʁɑ̃swa veʁɔv]; 22 January 1962 – 29 September 2021), also known as Le Grêlé ([lə ɡʁɛle, ɡʁele], the "Pockmarked Man"), was a French serial killer, rapist and police officer who murdered at least three people between 1986 and 1994 in the Île-de-France region. He received his nickname from acne scars seen on his face by witnesses following his first murder. Vérove committed suicide in September 2021 upon realizing that he was about to be identified.
Vérove's first murder, that of 11-year-old Cécile Bloch, took place in the 19th arrondissement of Paris in 1986. The following year he murdered two adults in the 4th arrondissement. He was linked to two further murders in 1991 and 1994, as well as two rapes in 1987 and 1994. During his crime spree, Vérove belonged to various French police forces; he was a member of the National Gendarmerie between 1983 and 1988, serving as a motorcyclist in the Republican Guard, then became an officer in the National Police in Paris until his retirement in 2019. He briefly held elected office as a municipal councillor in Prades-le-Lez, Hérault, between 2019 and 2020.
On 24 September 2021, Vérove received a police summons to provide a DNA sample as part of an investigation into the Bloch killing. His wife reported him missing on 27 September. Two days later, Vérove killed himself by barbiturate overdose in a rented flat in Le Grau-du-Roi, Gard. He left behind a suicide note in which he confessed to his crimes.

Beltrán Dalay Cortés Carvajal (21 November 1908 – 11 June 1984) was a convicted Costa Rican murderer, mostly known for the murders of the physicians Ricardo Moreno Cañas and Carlos Echandi. He is one of the most famous former prisoners of San Lucas Island.