I don’t want to be partisan but the most striking example I remember was when Comey weighed in on Secretary Clinton’s email server saying “there was no criminal intent”
If you’re ignorant of the law, you cannot have a criminal intent, or am I missing something?
In USA if police doesn't know it breaks your rights it cannot be sued directly. Qualified immunity I think. So ignorance is a shield if you have a shield.
This is a misstatement of the rule. Qualified immunity applies if the alleged action would not have violated a "clearly established Constitutional right", which does not depend on the personal knowledge of the individual being sued. (It's also applies to all public employees/officers, not just police, though its application in the domain of policing has frequently been controversial.)