John Ingvar Lövgren was born on October 22, 1930, in Sweden. He had a difficult childhood, as both of his parents died when he was very young. After their deaths, he was placed in a foster home. 

As an adult, Lövgren struggled with alcohol issues. He became known for drinking heavily, which led him into trouble with the law. He was convicted several times for exposing himself to women. His behavior raised concerns among the authorities, and he spent time in various psychiatric hospitals between 1953 and 1961. Those who worked with him found him to be childish and weak, and some believed he had a mild intellectual disability. During this time, Lövgren worked as a gardener.

John Ingvar Lövgren was a serial killer in Sweden who committed several murders between 1958 and 1963. His crimes began with the murder of Agneta Nyholm on June 27, 1958. She was 26 years old and was found dead in her home in Fruängen. This case remained unsolved for many years until Lövgren later confessed to it.

The following year, in November 1962, Lövgren murdered Greta Löfgren, a 62-year-old woman, in her home at Kungsholmen. He raped and killed her, adding to the sinister nature of his actions. His next victim was 6-year-old Berit Glesing. She was raped and murdered on August 12, 1963, in Vita Bergen at Södermalm.

Just a few weeks later, on September 2, 1963, Lövgren murdered a 4-year-old girl named Ann-Kristin Svensson in Aspudden. The child was also raped before her death. After this crime, playmates of Svensson identified Lövgren as the killer. In his attempt to escape, he discarded Svensson's clothes, which led police to his living area.

Lövgren was arrested soon after the murder of Ann-Kristin Svensson. After his arrest, he confessed to all four murders. While he was charged and convicted for these crimes, he was never convicted for the earlier murder of Agneta Nyholm, as her case had since become statute-barred, although law enforcement considers it solved with Lövgren as the prime suspect.

As a result of his crimes, Lövgren was sentenced to closed psychiatric treatment at Salberga prison. He became known as "Flickmördaren," which translates to "The Girl Killer" because two of his victims were young girls. Lövgren died in prison on February 9, 2002.