Connett
If you haven't already....
Have a look at AN903 9/6/95. A DH8 accident in New Zealand.
Police took out their own investigation, (in parallel to TAIC) and after almost 10yrs brought criminal proceedings against the Captain. It all got thrown out fairly quickly, but there was a long court case over police getting access to the CVR, which they got in the end. This resulted in almost all CVR's being deactivated in NZ for a few years, until futher protective legislation was enacted.