NASHVILLE, Tenn. (WKRN) - Key evidence was shown for the first time Wednesday in the case of a security guard accused of assaulting a man outside of a Demonbreun Street bar. In February, Austin Turner was left in a coma and died a couple of weeks after an altercation with Richard Cornelius, a licensed Tin Roof security guard. During a preliminary hearing Wednesday, May 1, Austin's family watched the video capturing the incident for the first tim…