It is also possible to apply a higher standard to the government employees and force greater transparency on them, up to treating them as de-facto slaves of the society.

Yeah okay, different standard just for government employees... So consider the same scenario above except instead of a cop its the son of a politician or the nephew of a billionaire. Not government employees. Are you comfortable with the government running secret trials for them too? Are you confident that the system can provide fair and impartial judgments for such people when nobody is allowed to check their work?