It's really worth reading up on the Ansett New Zealand DHC-8 crash and the resulting legal shenanigans, the behaviour of the police was bloody outrageous once they had been granted access to the CVR/FDR data.
Basically the police prosecutor made some kind of personal vendetta out of it, pursued the captain and dragged him through several court cases and appeals and counter appeals and all kinds of court cases for SIX YEARS after the event, long after the accident investigators had finished their work. He was finally cleared of all charges in the High Court.
This happened despite furious opposition from ALPA, and widespread negative publicity and debate in the NZ media at the time, about whether this was an effective use of police resources and what exactly they were trying to achieve. The law was subsequently changed in NZ to prevent CVR data being used in future police prosecutions, but the damage was certainly done, to that captain at least.
It also led to an unofficial practice among many NZ pilots, of pulling the CVR circuit breaker as part of their pre flight checks.
So much good work and advancement in the field of flight safety can be undone so quickly by the actions of one idiot lawyer, if the trust is broken down