" Using nothing but a teenager’s wand and Expelliarmus, Draco and Harry brought down the most powerful wizards of their age and survived. Both of them had cast the Cruciatus and Imperius curses, sometimes of their own volition and sometimes to protect others. But as he vowed to Narcissa and, posthumously, Lily, Snape’s efforts ensured that both Draco and Harry turned away from killing and kept their souls intact. "

― Lorrie Kim , Snape: A Definitive Reading