The right to a fair and impartial judiciary is given. It a fundamental right bestowed upon us by the Fourteenth Amendment to the Constitution. It is part of the Due Process of law that every person in this country is entitled to when charged with a criminal
In Ohio, impartiality of state judges is codified and discussed in the Ohio Code of Judicial Conduct
to which all judges are required to adhere or face severe sanctions. You want to look at Canon 3, though Canon 2 discusses impartiality at great length as well.
The fact that police are allowed to lie and use coercive and deceptive means to ferret out crime comes from the line of US Supreme Court
cases that started with Frazier v. Cupp in 1969
. In that case, some deception by the police caused the suspect to confess a homicide of which he was later convicted. The court ruled that, depending on the facts and circumstances of a particular case, such behavior is permissible. There's a good overview of this case and what it started here
That doesn't mean that police are required to lie and deceive or that lies and deceptions are always acceptable. Such things are challenged on a case-by-case basis, and a police officer can be determined to have gone too far and violated a defendant's rights. But the US Supreme Court formally recognizes that such activities by the police can be reasonable given their responsibility to seek out crime.
Police Internal Affairs is where police matters first get investigated, and complaints
against the police are taken very seriously in this department. From there, your State Attorney General is charged with dealing with corruption in state agencies, and ultimately the FBI can does involved, but generally only when the corruption is so widespread in the aforementioned agencies that they are perpetuating or condoning the unlawful conduct. In other words, the FBI doesn't step on state toes without a very good and clear reason.
Hope this helps.