Dagmar Overbye took in unwanted children – and killed them in horrific ways. The directer of The Girl With the Needle explains why he brought the story of ‘The Angel Maker’ to the big screen

The citizens of Denmark enjoy a reputation for living an exceptionally stress-free existence. This is in large part due to the small Scandinavian state’s unusually simple system for accessing government services. Every Dane or Danish resident has a CPR (Central Person Register) number made up of their date of birth and four extra digits that is used for anything from banking to tax returns, healthcare and borrowing library books.

It’s a boon of convenience with a grim backstory: Danish welfare services are so streamlined because since 1924 councils have been forced by law to keep population registers, a measure that was catalysed by one of the most gruesome serial murders in the country’s history. Three years earlier, 33-year-old Dagmar Overbye was found to have killed nine infants in her care (and was suspected of murdering 17 more), most of them foster children whose disappearance had not shown up in the national records.