These Officers responded in an agressive military manner without knowing what the situation was.
Their rules of engagement were that of an Infantry squad assualting a position in a combat zone. This is appropriate for Irag or Afganistan. It is not appropriate for Fulton county GA.
Shooting had ceased prior to their arrival. They had time to assess the situation before they opened fire on an unknown individual in and unknown situation. The list of unknowns was far greater than what they knew. In fact they had two knowns 1) shots had been fired. 2) An individual had a weapon. Just off the top of my head I can think of 10 or 20 unknowns which should have been addressed before they opened fire.
Many times we have seen standoffs go on for hours while police determined what the situation was. These generally end in a positive manner. Here a bunch of hot shot bad asses did not think. They lacked effective command and control. I would lay odds that the officers violated volumns of departmental procedures and regulations.
Look at the Miami Dade response to the FBI shoot out. Shots were being exchanged. The local Law enforcement could not determin what the situation was so they held position and waited until they could determine who and what was going on. This is the response which should have occurred in this incident.