This is about as good a smoking gun as you're gonna get:

CBS News learned that in 2009, the Tulsa Sheriff's Office launched an internal investigation to find out if Bates received special treatment during training and while working as a reserve deputy. They also investigated whether supervisors pressured training officers on Bates' behalf.

The investigation concluded Bates' training was questionable and that he was given preferential treatment.

The investigation found that deputies voiced concerns about Bates' behavior in the field, almost from the very beginning. Bates reportedly used his personal car while on duty and made unauthorized vehicle stops. When confronted Bates said that he could do what he wanted, and that anyone who had a problem with him should go see the sheriff.