He began killing in 1955, after his mother died. Around 1960, Kroll went to Duisburg and found work as a toilet attendant for Mannesmann. Afterwards he worked for Thyssen Industries and moved to Friesenstrasse 24, Laar, a district of Duisburg. At that time he resumed killing people.
1956 - Erika Schuletter, 12, raped and strangled in Kirchhellen which is now part of Bottrop.
16 June 1959 - Klara Frieda Tesmer, 24, murdered in the meadows of the Rhine, near Rheinhausen. A mechanic, Heinrich Ott, was arrested for the crime. He hanged himself in jail.
26 July 1959 - Manuela Knodt, 16, raped and strangled in the City Park of Essen. Slices of flesh were carved from her buttocks and thighs.
4 June 1962 - Monika Tafel, 12, killed in Walsum, slices of flesh carved from her buttocks. Walter Quicker was arrested for the crime. He was later released, but was driven by neighbors to suicide in October.
22 August 1965 - Hermann Schmitz, 25, and his girlfriend Marion Veen were attacked as they sat in a car in a lover's lane in Duisburg-Großenbaum. Hermann—Kroll's only male victim—was killed, but Veen escaped.
21 May 1970 - Jutta Rahn, 13, strangled walking home from a train station. Peter Schay was arrested and eventually released. He confessed to the crime in 1976 after being hounded by his neighbors.
8 May 1976 - Karin Toepfer, 10, raped and strangled in Voerde.
3 July 1976 - Marion Ketter, 4. Parts of her body were in the process of being simmered when Kroll was arrested.
Method
Kroll was very particular about where he killed, only killing in the same place on a few occasions years apart. This, and the fact that there were a number of other killers operating in the area at the time, helped him to evade capture. Kroll would surprise his victims and strangle them quickly. Afterward he would strip the body and have intercourse with it, often masturbating over it again. He would then mutilate and cut off pieces to be eaten later. Upon returning home, he would have intercourse again with a rubber sex doll he had for this purpose.
Capture
On 3 July 1976, Kroll was arrested for kidnapping and killing a four-year-old girl named Marion Ketter. As police went from home to home, a neighbor approached a policeman and told him that the waste-pipe in his apartment building had blocked up, and when he had asked his neighbor, Kroll, whether he knew what had been blocking the pipe, Kroll had simply replied, "guts". Upon this report, the police went up to Kroll's apartment and found the body of Marion Ketter cut up: some parts were in the refrigerator, a small hand was cooking in a pan of boiling water and the entrails were found stuck in the waste-pipe. Kroll was immediately arrested.
Trial and death
He admitted killing Marion Ketter and gave details of 13 other murders and one attempted murder over the previous two decades. Kroll said that he often sliced portions of flesh from his victims to cook and eat them, claiming that he did this to save on his grocery bills. In custody, he believed that he was going to get a simple operation to cure him of his homicidal urges and would then be released from prison. Instead he was charged with eight murders and one attempted murder. In April 1982, after a 151-day trial, he was convicted on all counts and was given a life sentence. He died of a heart attack in 1991 in the prison of Rheinbach.
