It is not so easy to change the internal investigation process as confidentiality also shields the investigations and results from internal personnel. Officers are told that discussing the investigation or discussing the incident at all can result in discipline up to and including termination. The internal trauma can be debilitating. When I suffered politically motivated claims of malfeasance (potentially criminal and certainly likely to end my career if sustained) I was prohibited from speaking to anyone at all besides my legal representative. I could not explain to my wife and children why I was so pissed off and acting out, I couldn't talk with a therapist or my minister, I had no release. This is NOT uncommon for many officers subject to political investigations. The agency may seek to nail the offending officer on a policy violation rather than on the internal hit he is being investigated for as it solves their problem. He talked, he's fired ...no need to show that he violated policy. In my case, my attorney negotiated a deal allowing me to speak with my pastor and my wife on the matter, and ultimately ALL the allegations were determined to be unfounded (as the investigation was done by an outside agency and not internally ... which would have been tough since I WAS the IA investigator! (They also violated my POBR rights but I lacked the fiscal resources to sue over that matter ... $25,000 retainer just to play.)
I don't know how it is in other states, but in CA money talks, and defending yourself against false allegations and politically motivated claims is nearly impossible unless you are indepentently wealthy, or you have a large association willing to foot the bill (and most cannot).
Most associations - and, certainly, most officers - lack the resources to actually sue over the internal investigation process, so correcting the process is a matter of political will.
Darrin Wilson is the incident that came to mind during my thinking on the matter. I also have personal experience to draw from as I was a union rep and union President for the better part of a dozen years and engaged my city in a pretty fierce battle concerning their persecution of an officer.

