Four cops to beat up a woman a full head shorter than any of them. The video shows no aggressive moves by Williams. It does show a normal response of trying to protect herself when being assaulted. Since there were no charges filed against her, the DA obviously concluded the same thing. Plus, the incident was pretty clearly covered up by the APD. 

What probable cause did they have to impound the car? That it was used to transport a gunshot victim? Not close to being sufficient.