No comment on the validity of this particular use of force. 
BUT the matter needs an entirely Independent investigation, just as SOP [standard operating procedure].  And by 'independent', I don't mean good buddies in the Dept of Law rubber stamping AST's representation of this [or any fatal] incident.
Dash cams and body cams are a Very good idea - perhaps the union might want to help cover the cost - as a means of protecting/justifying officers.  And it's past time to examine other possibilities for non-lethal officer protection, perhaps something that's not as easy, and tempting, to misuse as the taser.