sentence construction - Confused about "How could I have done this?"

This comes up while I am watching westworld. There is one scene in it. Teddy did some horrible things without consciousness. Then he backed to normal and asked Delores "How could I have done that?" Now I'm confused about this. As I learned from the grammar book, "could have done" is only used in unreal condition in the past or making a guess in the past. In this case, Teddy had already done the horrible things so the "unreal condition" explanation may not work. He also already knew the result so it's not like a guess either. Why didn't he say "How had I done that"? I'm puzzled here. Could anyone help share some insights on this? Thanks in advance.