"...it is a monstrous thing, to slay a unicorn," said Firenze. "Only one who has nothing to lose, and everything to gain, would commit such a crime. The blood of a unicorn will keep you alive, even if you are an inch from death, but at a terrible price. You have slain something so pure and defenceless to save yourself and you will have but a half life, a cursed life, from the moment the blood touches your lips."

Harry stared at the back of Firenze's head, which was dappled silver in the moonlight.

"But who'd be that desperate?" he wondered aloud.

...

"Can you think of nobody who has waited many years to return to power, who has clung to life, awaiting their chance?"

...

"Do you mean," Harry croaked, "that was Kob--"