Maria Catherina Swanenburg was born in Leiden on September 9, 1839, into extreme poverty, and lived in the Zijloord district, one of the poorest quarters of the city. She worked as a nurse and layer-out of the dead and was known to everyone as Goeie Mie, Good Mie, because she was always ready to sit with the sick and to help with a funeral.
Between 1880 and 1883 she poisoned more than ninety people with arsenic. At least twenty-seven died, including her own parents. She was the beneficiary of burial insurance policies she had taken out on them, sometimes several on the same person, and the sums were small: a few guilders each, which in that district was worth killing for.
Arsenic was sold openly as rat poison, and the symptoms were indistinguishable from the gastric illnesses that killed people constantly in a quarter with no sanitation. She was trusted, she nursed the dying, and she was in the house.
She was caught in December 1883 when a family she had been feeding all fell ill at once and a doctor tested the food. She was tried in 1885, convicted of three murders, which was all the evidence would carry, and sentenced to life. She died in prison at Gorinchem on April 11, 1915. She is the most prolific killer in Dutch history.