Dagmar Johanne Amalie Overby was born on April 23, 1887, in Denmark.

Dagmar Johanne Amalie Overby was a Danish serial killer who murdered between 9 and 25 children from 1913 to 1920. She was a child caretaker, looking after babies born out of wedlock. During her seven years of killing, she committed the crimes while caring for these children.

Dagmar used several methods to kill them. She strangled, drowned, or burned them in her masonry heater. After the murders, she would dispose of the bodies in different ways. Some were cremated, some buried, and others hidden in the loft of the buildings where she worked.

In 1921, Dagmar was convicted of nine murders. There was not enough evidence to prove the others, even though it was believed that she may have killed more children. Her lawyer argued that she had been abused as a child, hoping this would influence the court's decision. However, this did not have an effect on the judge.

On March 3, 1921, Dagmar was sentenced to death. This case was significant in Danish history and led to changes in childcare laws. She was one of only three women in the 20th century in Denmark to receive a death sentence, but her sentence was later changed to life imprisonment.

Dagmar died in prison on May 6, 1929, at the age of 42. Notes and artifacts related to her case can be found at the Politihistorisk Museum in Copenhagen.