This was how they knew.
Disclaimer: I obviously don't own Harry Potter.
They find Draco Malfoy half-dead in his ministry holding cell, supine in a pool of blood, his Dark Mark and several layers of skin and tissue beneath it scratched beyond recognition, perhaps beyond repair. His mother in the next cell had heard nothing, but had woken in the early morning, she said, with more dread in her heart than she had ever felt during the Dark Lord's reign. The wounds were non-magical, and the healing straightforward, but all that remained of the Mark was a ragged scar and a sliver of snake tongue, and this was how they knew for sure that this time, You-Know-Who would not be returning.