In general, a client waives solicitor-client privilege when he voluntarily transmits privileged communications to third parties.  The renunciation of the common defence doctrine is essentially the same as the renunciation of the right of the agent. The only difference is that the disclosure of a co-accused with the other lawyer is not a waiver of the confidentiality of that communication. Voluntary disclosure of allegedly privileged communications to third parties has long been considered incompatible with privilege. It is well established that when a party voluntarily transmits privileged communications to a third party, it waives the privilege.  Similarly, where a party discloses some of the otherwise privileged material, but retains the remainder, it waives privilege only with respect to actual disclosures, unless a partial waiver is unfair to the party`s opponent.  Disclosure alone may constitute, without premeditation, the waiver of solicitor-client privilege. … “According to the traditional doctrine of waiver, voluntary disclosure… a third party waives solicitor-client privilege, even if the third party agrees not to pass the communication on to third parties.  In Massachusetts, if a lawyer represents more than one client in a particular case, disclosure from a client to the lawyer in the presence of the other client is not privileged, as between clients.  In Thompson v. Cashman, a lawyer who worked for both the plaintiffs and the defendants, was allowed to testify during an interview between the lawyer, the complainant and the defendant.
  But not all disclosures lead to a waiver. “Under the privilege of the common defence, communication between the client and his or her own lawyer remains protected by solicitor-client privilege when disclosed to the co-accused or their counsel for common defence purposes.”    In Stepney, several defendants had been charged with violating several federal drug and gun laws. In an effort to effectively prepare a coherent defense, the defender attempted to take a JDA. It was about the court. In practical terms, these were the large number of accused, their lack of familiarity with each other and the many and varied criminal complaints involved in the case. The court was also rightly concerned about the murder of an accused. And the label itself, “joint defense,” is a little misleading, because the doctrine can be applied to non-judicial hiring, such as transactional communication. For this reason, the privilege of common defence is sometimes referred to as a “privilege of common interest.” Although joint defence agreements can be concluded orally, a common defence agreement should always be written and verified and signed by the client. United States v Stepney, 246 F.
Supp. 2d 1069, 1080 (N.D.Cal. 2003). A common problem with JDAs is the risk that a co-accused will decide to cooperate with the government.