Johannes Marinus van Zon was born on April 20, 1942, in Utrecht, Netherlands. He was often called Hans by people around him. Growing up, Hans was seen as a neat and charming young man. People described him as intelligent, but he struggled with laziness. This laziness often led him to have little money to support himself.

By 1967, Hans was in a relationship with a 47-year-old woman named Caroline Gigli. Caroline took care of him during this time. At the same moment, he was also involved with another woman, Coby van der Voort, who was 37 years old. Hans earned some money by selling pornographic photos of both women.

Though Hans had some charm, his relationships became complicated. After his relationship with Coby ended in April 1967, he accused her of continuing to impose on him. This tension led to serious decisions in his life.

Johannes Marinus van Zon committed several murders between April and August 1967. His first victim was Coby van der Voort. After their relationship ended, van Zon claimed she continued to bother him. On April 29, he entered her home and killed her using a lead pipe he made himself. To hide the crime, he mutilated her body to make it appear as if a robbery had taken place. He then gave the stolen jewelry to his girlfriend.

Later, van Zon confessed his crime to Arnoldus "Old Nol" Rietbergen, a criminal from Utrecht. Rietbergen directed van Zon to commit two robberies and one attempted robbery. He used a hollow stick with a concealed switchblade as his weapon. The victims of the two murders he committed during this time were Jan "Uncle Cupid" Donse, an 80-year-old shopkeeper, and a milkman named Reijer de Bruijin. Both of these murders took place on May 31 and August 12, respectively.

Van Zon also attacked Dora Woortmeijer, a widow and former lover of Old Nol, in an attempted robbery. He struck her with the lead pipe and left her for dead, but she survived and identified him later. A tip from the Utrecht underworld helped lead to his arrest on December 13, 1970. In March 1970, he was sentenced to life imprisonment. He was also suspected of several other murders, including the killings of Elly Segov in 1964 and English film director Claude Berkeley in 1965.