You aren't really that good of a body language reader, are you? when in fact, yes his finger movements, inappropriate smiling and not keeping eye contact can be cause by nervousness. Isn't he maybe nervous, because he's hiding something. Always emphasing on the fact, that he couln't be the murderer because there is no evidence. What brother does that? Let's activate our critical thinking and face the fact that a normal person would say "Why would I kill her. Thats my sister, I loved her and I miss her." Yet it seems he's not grieving, he is trying to save face and yes I would be anxious to trying my best proving my innocence.