Type in Elizabeth Bathory in Google. Go one go ahead, I'll wait.
Now when you read about her what comes to mind, the 600 young girls she apparently killed? Or the idea that she did it so sadistically? or, that she wasn't stopped?
I'll give you my version as to why she wasn't stopped:
Many of the girls whom she killed were servants or girls from nearby villages. Nobility possibly didn't take much notice in that, and it could be argued that the girls "went" to another village, although this would be unlikely since this happened within the borders of the Carpathian mountains, in Transylvania, in the 1600s.
The way people, or more specifically, the nobility found out about her deeds was when she began to take daughters of the minor nobility to her castle to kill them. That was when the investigation began and they found the evidence they needed. A young woman dying on the floor in the cellar mass graves and a list of 600 or more names of young women, who the countess later admitted she and her associates killed.
Which bring me to the next question what about her associates? Were they Walled up with her?