[russellallen]

The general rule in Common Law (English speaking) legal systems is that if the lawyer knows (as opposed to suspects) that their client is guilty, they cannot let their client plead not guilty. They can still defend the client by pleading for a lesser sentence etc, or they can cease acting for the client. They don't have any obligation to tell the court, just an obligation not to lie to the court. Of course each jurisdiction will have its own rules about this.

[powera]

Except you don't enter a plea for an action, you enter a plea for a criminal charge. A murderer can confess a crime to his lawyer (under privilege), and still honestly plead not-guilty to first-degree murder (for example, it could be considered manslaughter).