The Chestnut Man
The Chestnut Man is a 6-part Danish crime thriller which opens with the murder of a family in 1987. There are foster children in the family who are not killed.
More than 30 years later, detectives investigate the brutal murder of a young woman whose son is now in the foster care system.
As the series proceeds we find out that one man has decided the child protection system is inadequate and he has become a vigilante on behalf of neglected children.