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"We wished to keep you and Harry apprised of recent developments," said McGonagall. "Magical Law Enforcement has been interrogating the Death Eaters who were captured at Gringotts. One thing has come to light: all of them were ordered by Bellatrix to avoid using the Killing Curse at all costs."

"Right. Because they're so merciful and all," snorted Ron. "They weren't making any effort to avoid killing people at Gringotts. They killed Seamus and Lavender! They used the Killing Curse then!"

"But that was when Bellatrix made her Horcrux," said Hermione thoughtfully. "Oh, thank you, Harry, you're an angel," she added, as Harry stepped into the portrait bearing two cups of hot cocoa.

Harry kissed her as he surrendered one of the cups. Ron smirked and shook his head sadly.

"Don't start," Harry warned him, and took a sip. After a moment he looked up. "Ron, tell me again about when Voldemort killed us. Didn't he say something about the Curse to Bellatrix…?"

"Yeah," Ron admitted, losing his smile. He would never be happy recalling the memories of that day. "He told her that, uh, the Killing Curse was his alone."

"Right, so maybe that's why the current crop of Death Eaters isn't using it," said Harry. "Bellatrix gave them the same order that Voldemort gave her. Makes sense, if she sees herself as Voldemort's successor…"

"I don't think so, Harry," Hermione mused. "Avada Kedavra is terrible, terrifying… a potent weapon for fear-mongers. They'd never give up using it without a good reason. And even Bellatrix gave up using it – she didn't use it at Gringotts – but she did use it when she murdered Lavender. To make a Horcrux."

"Ahhh, I see," said McGonagall. "Horcruxes require the soul to be fractured by committing murder. You're suggesting that the murder needs to be done with the Killing Curse?"

"As opposed to, say, burning someone to death with Incendio. Exactly. The Killing Curse is driven by the pure desire to kill – that's what makes it Unforgivable. And if you want someone dead that badly, you're halfway to fracturing your soul already."

"I think all of the murders Voldemort used to make Horcruxes were done with Avada Kedavra," added Harry, counting on his fingers. "His parents, Hepzibah Smith, old Frank Bryce…"

"You," she added. "Or at least that was his intent."

"And even if your theory's wrong, love, it only matters that Bellatrix thinks Horcruxes need Avada Kedavra."

"So you think Voldemort wouldn't let his followers use the Killing Curse because they might make their own Horcruxes? And Bellatrix is doing the same now?" Ron whistled and shook his head. "Suppose we shouldn't complain. I mean, as long as they're not using the Curse, it doesn't matter why."

"We can take some comfort in the fact that Bellatrix doesn't come close to matching Tom Riddle's raw power,"

http://www.fanfiction.net/s/7024025/13/