[It's more that he's frustrated at the lack of accurate information to report than any guilt at not being able to remember his actions. In fact, he's confused at first, as to what could possibly be "troubling" about anything he could remember. He's about to ask for clarification on what Chilton means, when he suddenly thinks back to that moment in Orochimaru's hideout with Naruto and Sakura, and their reactions to the false story he had told them, about his mission being to engineer Konoha's destruction so that it could be rebuilt in Danzou's image. They were angry, as they told him about all the people who would die, all the suffering it would cause. At the time, it had meant nothing to him. People died in war, that was just how it was. But even if he's still incapable of empathizing with humanity in the abstract, he has a little better of an idea of where Naruto and Sakura were coming from: people would be upset at losing their bonds.

He connects the dots, then, about what Chilton is really asking.]

I'm not certain you realize how many people I've killed fully of my own volition, Frederick-san.

[There might be just as much blood or more on this boy's hands as Hannibal's, honestly, if one takes that entire bingo book of assassination targets into account.]

I have been a weapon for a very long time, for far longer than I have attempted to be an individual. It would be unfortunate if I had killed someone for no reason, true, but it is not as if I would have held objection to doing so if it had been necessary, even now.