sells knew victims

“Is there anything else you could tell me that would be of use?”
“Yes. The killer knew the victims. And I’m thinking it was a woman.”
Carmichael snorted. “I don’t believe we got to sit here and listen to this. Nine times out of ten the killer knows the victim.”
“Shut up, Carmichael,” Murphy said. “What makes you say that, Harry?”
I stood up, and rubbed at my face with my hands. “The way magic works. Whenever you do something with it, it comes from inside of you. Wizards have to focus on what they’re trying to do, visualize it, believe in it, to make it work. You can’t make something happen that isn’t a part of you, inside. The killer could have murdered them both and made it look like an accident, but she did it this way. To get it done this way, she would have had to want them dead for very personal reasons, to be willing to reach inside them like that. Revenge, maybe. Maybe you’re looking for a lover or a spouse.
“Also because of when they died—in the middle of sex. It wasn’t a coincidence. Emotions are a kind of channel for magic, a path that can be used to get to you. She picked a time when they’d be together and be charged up with lust. She got samples to use as a focus, and she planned it out in advance. You don’t do that to strangers.”
“Crap,” Carmichael said, but this time it was more of an absentminded curse than anything directed at me.
Murphy glared at me. “You keep saying ‘she,’” she challenged me. “Why the hell do you think that?”
I gestured toward the room. “Because you can’t do something that bad without a whole lot of hate,” I said. “Women are better at hating than men. They can focus it better, let it go better. Hell, witches are just plain meaner than wizards. This feels like feminine vengeance of some kind to me.”
“But a man could have done it,” Murphy said.
“Well,” I hedged.
“Christ, you are a chauvinist pig, Dresden. Is it something that only a woman could have done?”
“Well. No. I don’t think so.”
“You don’t think so?” Carmichael drawled. “Some expert.”
I scowled at them both, angry. “I haven’t really worked through the specifics of what I’d need to do to make somebody’s heart explode, Murph. As soon as I have occasion to I’ll be sure to let you know.”

Storm Front Chapter 2, Page 18-19