Joachim Kroll was born on April 17, 1933, in Hindenburg, Germany (now Zabrze, Poland), the youngest of eight children in an impoverished mining family. His father was captured by Soviet forces during World War II and never returned, leaving the family destitute. Kroll was described as intellectually disabled, with an IQ estimated between 76 and 80. He worked menial jobs as an agricultural laborer and later in a factory, living a solitary existence in small apartments. His unremarkable appearance and quiet demeanor allowed him to evade suspicion for over two decades while he committed horrific crimes across the industrial Ruhr region.

Kroll's victims ranged from young children to elderly women, selected primarily for their vulnerability. His first confirmed killing occurred on February 8, 1955, when he raped and stabbed 19-year-old Irmgard Strehl in a barn near Walstedde. Over the following years, he continued his predatory pattern, targeting victims in parks, forests, and isolated areas. Among his youngest victims were four-year-old Marion Ketter, whose disappearance in 1976 would ultimately lead to his capture, and eight-year-old Monika Tafel, murdered in 1962. Kroll confessed to 14 murders, though investigators suspected he may have been responsible for additional unsolved cases throughout the region.

The investigation into Kroll's crimes was hampered by jurisdictional fragmentation across multiple German police departments and the rudimentary forensic capabilities of the era. Tragically, innocent men were wrongly convicted of Kroll's murders on at least two occasions. Walter Quicker was suspected in the 1959 murder of Manuela Knodt and died by suicide before trial, while Vinzenz Kuehn served six years in prison for a 1966 double murder that Kroll later admitted committing. These miscarriages of justice highlighted the systemic failures that allowed Kroll to continue killing for so long.

Kroll's arrest on July 3, 1976, came about through a grotesque discovery. A plumber called to investigate a blocked toilet drain in Kroll's Duisburg apartment building found the pipe clogged with human organs. When police questioned Kroll, he matter-of-factly explained that the remains belonged to Marion Ketter, a four-year-old girl who had vanished from a nearby playground that day. A search of his apartment revealed parcels of human flesh in his refrigerator and a child's hand cooking in a pot of vegetables on the stove. Kroll admitted to practicing cannibalism, stating he consumed human flesh to save money on groceries.

Kroll's trial began on October 4, 1979, in Duisburg and lasted 151 days, making it one of the longest criminal proceedings in German history. Despite defense arguments regarding his mental capacity, Kroll was found legally responsible for eight murders and one attempted murder. On April 8, 1982, he was sentenced to nine concurrent life terms with no possibility of parole. He expressed no apparent remorse during proceedings and seemed disconnected from the gravity of his crimes. Kroll died of a heart attack in Rheinbach Prison on July 1, 1991, at age 58.

The Kroll case remains significant in criminal justice history for several reasons. It exposed critical flaws in German police coordination and forensic investigation methods, prompting reforms in inter-agency communication. The wrongful convictions of innocent men underscored the dangers of tunnel vision in murder investigations. Criminologists have studied Kroll extensively as an example of how individuals with lower cognitive function can nonetheless evade detection through patient, opportunistic offending. His case also contributed to understanding the psychology of sexual sadism and cannibalistic behavior, joining the ranks of Germany's most disturbing serial murder cases alongside those of Fritz Haarmann and Karl Denke.