Dagmar Johanne Amalie Overbye was born on April 23, 1887, in Denmark. Information about her early childhood is limited, though it was later suggested by her defense counsel that she herself may have been subjected to abuse as an infant. This claim, however, was not substantiated to the satisfaction of the court and did not influence the final judgment against her.

As an adult, Overbye worked as a professional caretaker for infants born outside of marriage. During the early twentieth century, unmarried mothers in Denmark often faced intense social stigma, leading many to place their newborn children in private care arrangements. Overbye presented herself as someone willing to adopt or care for these children in exchange for payment, exploiting a vulnerable population during a period when oversight of such arrangements was minimal.

Outwardly, Overbye appeared to operate within the bounds of informal childcare practices common at the time. In reality, her occupation provided her access to infants whose disappearances were unlikely to be immediately questioned, particularly given the social marginalization of their mothers. This environment allowed her crimes to continue for years without detection.

Between 1913 and 1920, Dagmar Overbye murdered a number of infants entrusted to her care. The victims were babies born out of wedlock, left with Overbye by mothers who believed she would arrange adoption or long-term care. Instead, Overbye systematically killed the children.

She employed several methods of murder, including strangulation, drowning, and burning. Some of the infants were killed in her home, with their bodies burned in her masonry heater. Others were buried, cremated, or concealed in the loft of her residence. The crimes remained largely undiscovered for years due to the lack of records and the social isolation of the mothers involved.

Authorities eventually uncovered Overbye’s actions, leading to her arrest and prosecution. During the investigation, it was suspected that she may have murdered between nine and twenty five children, including at least one of her own. Due to insufficient physical evidence, prosecutors were only able to secure convictions for nine murders.

On March 3, 1921, Overbye was convicted and sentenced to death in one of the most significant criminal trials in Danish history. The case drew widespread public attention and ultimately prompted changes in legislation related to childcare and adoption practices in Denmark. Although she was sentenced to death, her sentence was later commuted to life imprisonment, making her one of three women in Denmark during the twentieth century to receive a death sentence that was ultimately reprieved.

Dagmar Overbye remained incarcerated for the remainder of her life. She died in prison on May 6, 1929, at the age of forty two. Records and materials related to her case are preserved in the Police History Museum in Nørrebro, Copenhagen, reflecting the lasting impact of her crimes on Danish legal and social policy.