Problem: Dershowitz is missing the reason why this became a national story in the first place. Had Zimmerman been arrested on the fateful night, this current discovery/autopsy process would have begun immediately.
http://www.slate.com/blogs/weigel/2012/05/18/george_zimmerman_s_blood.html
So, make the arrest, THEN determine if there is evidence to charge the guy.
Lefties are the smartest people in the world. Just ask them and they'll tell you.
Um, Zimmerman WAS arrested on the night in question.