"Because I lost control. She was harping on about what a cute couple you and Granger made. It was sickening to see this bint get what was supposed to be mine. I lost it finally and assaulted Luna in that corridor. I hid myself in an alcove when I heard Granger coming down to check and in desparation used the opportunity to stun her, and then I used Granger’s wand to finish off the lunatic and blamed it on Granger. Everything was perfect after that, if only those meddling Death Eaters hadn’t foiled it by freeing her. I wanted to become Lady Potter and I did finally."