Sid Ahmed Rezala (13 May 1979 – 28 June 2000) was an Algerian-born French serial killer, dubbed "The Killer of the Trains". He was suspected of killing at least three women in 1999.

Waneta Ethel (Nixon) Hoyt (May 13, 1946 – August 13, 1998) was an American serial killer who was convicted of killing all five of her biological children.

James Warren Jones (May 13, 1931 – November 18, 1978) was an American cult leader, preacher, and mass murderer who founded and led the Peoples Temple between 1955 and 1978. Jones and the members of his inner circle planned and orchestrated a mass murder–suicide that resulted in the deaths of over 900 people including 304 children, which he described as "revolutionary suicide", a term coined by Huey P.

José Dorángel Vargas Gómez (born May 14, 1957), also known as "El comegente" (lit. The people eater), is a serial killer and cannibal in Venezuela.

Henry Oliver Rinnan (14 May 1915 – 1 February 1947) was a Norwegian Gestapo agent. Rinnan led a group called Sonderabteilung Lola in the area around Trondheim Municipality, Norway, during World War II.

Hastings Kamuzu Banda (c. 1898 or 1906 – 25 November 1997) was a Malawian politician who served as the leader of Malawi from 1964 to 1994.

Enrico De Pedis (Italian pronunciation: [enˈriːko de peˈdis]; 15 May 1954 − 2 February 1990) was an Italian gangster and one of the bosses of the Banda della Magliana, an Italian criminal organization based in the city of Rome, particularly active throughout the late 1970s until the early 1990s. His nickname was "Renatino".

The Pozzetto massacre was carried out by the same perpetrator at three locations in eastern Bogotá, Colombia on 4 December 1986. Over the course of seven hours, 29 people were killed and 11 others were injured by 52-year-old Campo Elías Delgado.

Milton Johnson (May 15, 1950 – May 16, 2025), known as The Weekend Murderer, was an American serial killer and mass murderer who was believed to have committed up to 14 murders that occurred in Will County, Illinois during the summer of 1983. Two of the victims were police officers.

Saizō Kishimoto (岸本 才三, Kishimoto Saizō; May 15, 1928 – January 17, 2014) was a Japanese gangster.

Koose Munisamy Veerappan (18 January 1952 – 18 October 2004) was an Indian poacher, smuggler, domestic terrorist and bandit who was active for 36 years, and kidnapped major politicians for ransom. He was charged with sandalwood smuggling and poaching of elephants in the scrub lands and forests in the states of Tamil Nadu, Karnataka and Kerala.

On May 24, 2022, a mass shooting occurred at the Robb Elementary School in Uvalde, Texas, United States, where 18-year-old Salvador Ramos, a former student at the school, fatally shot 19 students and 2 teachers, while injuring 18 others. Ramos was killed 77 minutes after entering the classroom by law enforcement officers.

Cuauhtémoc Gutiérrez de la Torre (born 16 May 1968) is a Mexican lawyer, politician and former waste picker leader from the Institutional Revolutionary Party (PRI). From 2010 to 2012 he served as a plurinominal deputy during the 61st session of Congress and, from 2012 to 2014, he served as president of the Institutional Revolutionary Party in Mexico City.

Herman Webster Mudgett (May 16, 1861 – May 7, 1896), better known as Dr. Henry Howard Holmes or H.

Richard Scott Baumhammers (born May 17, 1965) is an American spree killer and white supremacist who committed a racially motivated shooting spree on April 28, 2000, in the metropolitan area of Pittsburgh, Pennsylvania, killing five people and paralyzing one.

Pasquale Galasso (Poggiomarino, May 17, 1955) is a former boss of the Galasso clan, a clan of the Camorra, the Neapolitan crime organization. Since August 1992, he has been a pentito (a criminal turned state witnesses), collaborating with the Italian justice.

Terry Douglas Clark (May 17, 1956 – November 6, 2001) was an American murderer convicted of the murder of nine-year-old Dena Lynn Gore. He was executed by the state of New Mexico by means of lethal injection.

Herberts Albert Cukurs (17 May 1900 – 23 February 1965) was a Latvian aviator and Nazi collaborator. He served as the deputy commander of the Arajs Kommando, a collaborationist unit that carried out the largest mass murders of Latvian Jews during the Holocaust.

David Patrick Roger Lefèvre (born 17 May 1980), known as The Swamp Killer (French: Le Tueur des Marais), is a French serial killer.

Sergey Aleksandrovich Shipilov (Russian: Серге́й Алекса́ндрович Шипи́лов; born 17 May 1959), known as The Velsk Chikatilo (Russian: Вельский Чикатило), is a Russian rapist and serial killer sentenced to life imprisonment for 14 murders and nine rapes. Most of his murders took place in the town of Velsk.

Bartholomew Roberts (17 May 1682 – 10 February 1722), born John Roberts, was a Welsh pirate who was, measured by vessels captured, the most successful pirate of the Golden Age of Piracy. During his piratical career, he took over 400 prize ships, although most were mere fishing boats.

Salvatore "Sammy the Bull" Gravano (born March 12, 1945) is an American former mobster who rose to the position of underboss in the Gambino crime family of New York City before becoming a government witness. As the underboss, Gravano played a major role in prosecuting John Gotti, the crime family's boss, by agreeing to testify as a government witness against him and other mobsters in a deal.

Yegor Nikolayevich Khabarov (Russian: Егор Николаевич Хабаров; born May 18, 1979), known as The Electrician (Russian: Электрик), is a Russian murderer and suspected serial killer who was convicted of electrocuting at least two men in Yekaterinburg from 2008 to 2009, with the help of accomplice Sergey Kochnev. He was suspected in a total of seven deaths, but was never charged due to a lack of evidence.

Harvey Louis Carignan (May 18, 1927 – March 6, 2023) was an American serial killer who was sentenced to life in prison for the murders of two women in the early 1970s. He had been previously convicted of a 1949 rape and murder he committed while stationed in the U.S.

William Richard Bradford (May 18, 1946 – March 10, 2008) was an American convicted murderer and suspected serial killer and serial rapist who was incarcerated in San Quentin State Prison for the 1984 murders of his 15-year-old neighbor Tracey Campbell and barmaid Shari Miller. In July 2006, the Los Angeles County Sheriff's Department released a compilation of photos found in Bradford's apartment in the 1980s, depicting 54 different women in modelling poses.

The Moors murders were a series of child killings committed by Ian Brady and Myra Hindley in and around Manchester, England, between July 1963 and October 1965. The five victims – Pauline Reade, John Kilbride, Keith Bennett, Lesley Ann Downey and Edward Evans – were aged between 10 and 17, and at least four were sexually assaulted.

Anthony John Spilotro (May 19, 1938 – June 14, 1986), nicknamed "Tony the Ant", was an American mobster and high-ranking member of the Chicago Outfit who operated in Las Vegas during the 1970s and '80s. Spilotro managed the Outfit's illegal casino profits (the "skim") when four of the casinos, the Stardust, the Fremont, the Hacienda and the Marina, were managed by Frank "Lefty" Rosenthal, replacing Outfit member John Roselli.

Francisca Cortés Picazo (born 20 May 1955), more commonly known as "La Paca", is a Spanish drug lord, and matriarch of the Romani drug clan known as "La Paca" clan.

Nikolay Alekseyevich Soltys (May 19, 1974 – February 13, 2002) was a Ukrainian fugitive charged by the United States District Court for the Eastern District of California in a Federal Bureau of Investigation arrest warrant. The federal charges were for unlawful flight to avoid prosecution and there were California arrest warrants for six murders of his family members in and around the Sacramento area in August 2001.

Hamilton Howard "Albert" Fish (May 19, 1870 – January 16, 1936) was an American serial killer, rapist, child molester and cannibal who committed at least three child murders between July 1924 and June 1928. He was also known as the Gray Man, the Werewolf of Wysteria, the Brooklyn Vampire, the Moon Maniac, and the Boogey Man.

Pol Pot (born Saloth Sâr; 19 May 1925 – 15 April 1998) was a Cambodian politician, revolutionary, and dictator who ruled Democratic Kampuchea from 1975 until his overthrow in 1979. During his reign, his administration oversaw mass atrocities and he is widely believed to be one of the most brutal despots in modern world history.

On November 19–20, 2022, an anti-LGBTQ–motivated mass shooting occurred at Club Q, a gay bar in Colorado Springs, Colorado, United States. Five people were killed, and 25 others were injured, 19 of them by gunfire.

María de las Mercedes Bernardina Bolla Aponte de Murano (20 May 1930 – 26 April 2014), better known as Yiya Murano, and also referred to as The Poisoner of Monserrat was an Argentine serial killer and swindler. Convicted of three murders, she was imprisoned for 16 years before being sent to an elderly care facility to serve out the remainder of her sentence, due to her advanced age.

Lakireddy Bali Reddy (1937 – November 8, 2021) was an Indian and American landlord, convicted felon, and chairman of the Lakireddy Balireddy College of Engineering in Andhra Pradesh. Reddy exploited the Indian caste system to bring young Indian women and girls to Berkeley, California.

Émile "Mimile" Buisson (19 August 1902 – 28 February 1956) was a French gangster, and French public enemy No. 1 for 1950.

Roger Reece Kibbe (May 21, 1939 – February 28, 2021) was an American serial killer and rapist known as the "I-5 Strangler". Kibbe found all but one of his victims on freeways around Sacramento, California.

Giuseppe Giacomo Gambino (Palermo, 21 May 1941 – Milan, 30 November 1996), also known as u tignusu (the bald one), was a member of the Mafia and head of the San Lorenzo mandamento. Giuseppe Giacomo Gambino was considered the deputy of Totò Riina since the 1970s and the two frequently traveled together.

Richard Wayne Snell (May 21, 1930 – April 19, 1995) was an American white supremacist convicted of killing a pawn shop owner whom he mistook for a Jew and a black police officer in Arkansas on November 3, 1983, and June 30, 1984, respectively. Snell was sentenced to death for one of the murders and executed by lethal injection in 1995.

Francisco García Escalero (24 May 1948 – 19 August 2014) was a Spanish serial killer convicted for the murders of at least 11 individuals between 1987 and 1994. He also practiced necrophilia and cannibalism.

Angelo Bruno (born Angelo Annaloro, Italian: [ˈandʒelo annaˈlɔːro]; May 21, 1910 – March 21, 1980) was a Sicilian-American mobster who was boss of the Philadelphia crime family for two decades until his assassination. Bruno was known as "The Docile Don" due to his preference for conciliation over violence, in stark contrast to his successors.

Mengistu Haile Mariam (Amharic: መንግሥቱ ኀይለ ማርያም, pronunciation: [mənɡɨstu haɪlə marjam]; born 21 May 1937) is an Ethiopian former politician, revolutionary, and military officer who served as the head of state of Ethiopia from 1977 to 1991. He was General Secretary of the Workers' Party of Ethiopia from 1984 to 1991, chairman of the Derg—the Marxist–Leninist military junta that ruled Ethiopia—from 1977 to 1987, and president of the People's Democratic Republic of Ethiopia (PDRE) from 1987 to 1991.

Jeffrey Lionel Dahmer (; May 21, 1960 – November 28, 1994), also known as the Milwaukee Cannibal or the Milwaukee Monster, was an American serial killer and sex offender who killed and dismembered seventeen men and boys between 1978 and 1991.

Lam Kor-wan (Chinese: 林過雲; Jyutping: lam4 gwo3 wan4; born 22 May 1955) is one of Hong Kong's most notorious serial killers.

Kenneth Alessio Bianchi (born May 22, 1951) is an American serial killer, kidnapper, and rapist. He is known for the Hillside Strangler murders which he committed with his cousin Angelo Buono Jr.

Daniel Camargo Barbosa (22 January 1930 – 13 November 1994) was a Colombian serial killer and rapist. He is one of the most prolific serial killers in history and is believed to have raped and murdered at least 72 young girls in Colombia and Ecuador during the 1970s and 1980s.

Richard Trenton Chase (May 23, 1950 – December 26, 1980) was an American serial killer, cannibal and necrophile known as the Vampire of Sacramento, the Dracula Killer and the Vampire Killer, who killed six people between December 1977 and January 1978 in Sacramento, California.

Bonnie Elizabeth Parker (October 1, 1910 – May 23, 1934) and Clyde Chestnut "Champion" Barrow (March 24, 1909 – May 23, 1934) were American outlaws who traveled the Central United States with their gang during the Great Depression, committing a series of criminal acts such as bank robberies, kidnappings, and murders between 1932 and 1934. The couple were known for their bank robberies and multiple murders, although they preferred to rob small stores or rural gas stations.

Thomas James DeSimone (June 6, 1946 – disappeared January 14, 1979) was an American criminal associated with New York City's Lucchese crime family who is alleged to have participated in both the Air France robbery and the Lufthansa heist. It is believed DeSimone was responsible for participating in at least 5 murders, from William "Billy Batts" Bentvena in 1970, Michael "Spider" Gianco in 1970, William Reckhow in 1970, Ronald "Foxy" Jerothe in 1974, and Parnell "Stacks" Edwards in 1978.

Lorenzo Jerome Gilyard Jr. (born May 24, 1950), known as The Kansas City Strangler, is an American serial killer.

Alexander Nikolayevich Komin (Russian: Алекса́ндр Никола́евич Ко́мин, Aleksandr Nikolayevich Komin; 15 July 1953 – 15 June 1999), known as The Slaveholder (Russian: Рабовладелец, Rabovladyelyets), was a Russian enslaver and serial killer. At various times from 1995 to 1997, he kept six people as prisoners in a 9-metre-deep bunker under his garage.