[Xue Yang gives him a look that clearly says he doesn't have the time or interest in telling the whole story. Xue Yang always did what he was told and helped with things because it was fun and it was interesting. Not because he particularly cared what the reasons were.]

Power. Money. Revenge. Why does anyone do anything? The you of now doesn't have the reasons that the you of then did. And I'm not going to tell you what they were because it might be better for you if you don't know.

[He can claim innocence in that way. If he doesn't know why he did those things, then people will have a harder time holding him responsible.]