Sorry if this opinion has appeared here already, but I did not see it if so.
This 7th circuit case decided April 2012 contains a dense discussion of the conduct of a lawyer for an alleged bank robber who disclosed the client's intention to present a false alibi defense. The intention appeared in a sealed envelope the client asked the lawyer to deliver to a cousin. The lawyer opened the letter and discovered the plan. He disclosed it in a motion to wihdraw, as his reason to withdraw, without first trying to dissuade this client and without seeking to submit the motion under seal so the prosecutor was informed of the client's plan. The prosecutor then called the now former lawyer to testify against his client, who was convicted. The new (trial) lawyer did not object.
The opinion addresses both the confidentiality rule and its exceptions and the privilege. Posner joined by Rovner affirmed the conviction. Hamilton dissented, finding the lawyer's conduct unethical and ineffective assistance and finding the trial lawyer's failure to object to the former lawyer's testimony also ineffective.
Both opinions fault the procutor's strategic decision to call the former lawyer as essentially piling on. The majority writes that even if its opinion is wrong in every particular, the error was harmless, which Hamilton disputes.
Hamilton points out that the majority opinion would entitle a lawyer to go straight to the authorities whenever a criminal defendant suggests perjury or a fraud on the court in order to beat a charge, which he suggests correctly is not a rare occurrence. He writes at length to explain why that is and should be forbidden as a "first response" to the client's suggestion.
Hamilton has much the better argument and his opinion is grounded in the reality of criminal defense work and criminal adversary justice. Posner's opinion gives inadequate (actually almost no) recognition to the adversary system and the role of a criminal defense lawyer or to the consequences of allowing defense lawyers to do what the lawyer here did. He writes as though the lawyer's first and unqualified duty was to the court and so he was free to sound the alarm as soon as the client went looking for a false alibi witness.