On the first part, you're right, that's why witnesses are important as well, but you decided to ignore that part.
On the second part, I'm not searching for it because it was pages ago (Friday afternoon I believe) and I'm on my phone, but you said something similar to "if TM even caused GZ's injuries". Only way I take that is a) someone else was there that night, b) GZ already had those injuries, c) he self inflicted/faked them. I have read some theories on the self inflicted part, but they don't seem all that credible.