He apologizes for what seems like the tenth time and part of Katniss wishes he would stop, because saying it doesn't take back anything that happened. But now that she's been back to District 12, Katniss understands better than she ever thought she would and remembers how frantically she'd said the words in her mind, as if it would bring the dead skulls crunching under her feet back to life. I'm sorry I killed you. And you, and you, and you...

Well, it doesn't help. It's said to help the person saying it, she knows that now, because what good do the dead have for their useless words? "I know," Katniss breathes, and it's not said with spite at the very least. Even though they've been sleeping for two days, Katniss is tired and worn down in a way that she didn't think was possible.