I don’t know who did what, but it would not take technical expertise in tracking the hack to find out who did it. Intercepting communications chatter, human assets, etc can tell you who was responsible without any Internet digging at all I would think.
Not at all difficult when your own NSA did the deed. I got well flamed the other day for expressing this idea but the simple solution is that the NSA did the hack job on Sony and the Norks. They had the means and the opportunity and the Jug Eared field hand in the White Hut has the motive.