Let’s first remove the bias in policing and sentencing and parole and police killings (perhaps you are saying the police are justified in killing young black men and the mentally ill at 8X the demographic rate because the cops instantly know they are “lying”?), then we can start talking about whether the police and judges are after “truth” or whether it is just a bunch of bias-confirming BS. I’m surprised you didn’t mention the polygraph “tests” so beloved of police detectives. All the above “techniques” are predicated on the assumption that the person you are questioning is like you, which they are not.
How do we as a society detect when armed police lie, or fabricate or hide evidence, or refuse to disclose body-cam videos?