Thank you for my morning chuckle!
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.