DAs don't require the help and assistance of the police to make their cases.  The police bring them their (the police) case.  DAs require good police work, and the decision to no file a case occurs more than you think.  

If you watch the entire press conference, you will see just how thorough and professional this investigation was.  It is unfortunate that Ms. Gorrow did not mention the ear witness that heard the repeated demands by police to drop his weapon.  

What is VERY interesting is his attorney filed a tort claim notice without hearing all the evidence, relying only on her client's statement to her.  Or did she already know what was coming at the press conference?