"Once again, senseless slaughter has raised questions not only about how mentally disturbed people can obtain guns, but why authorities can’t intervene to prevent violence. Do the laws regarding mental health professionals’ duty to warn the authorities of a threat need to be toughened to make them more effective"The debate (available here) includes six authors, and I found interesting that they disagree as to what the state of the law is as to the duty of a therapist to disclose information. This, in itself, I think shows that there is no agreement on the subject.
One author, for example, states that "[i]n most states, a psychiatrist or psychologist can only inform law enforcement officials about patients who "pose a clear and present danger to himself, herself, or to others"" while another author states that "[a]lmost all states have laws that either require or permit mental health professionals to disclose information about patients who may become violent." Interestingly, in this case, both authors agree that whatever the duty is, it needs to be broadened. One of them proposes that "every state should have a mandatory duty-to-protect statute that takes effect even when there is no identifiable potential victim" which is the highest duty possible, one I am not sure therapists would agree is a good idea.
The reason for the confusion is due, at least in part, to the fact that contrary to what is usually assumed, Tarasoff v Regents of the University of California, a case pretty much everyone reads in law school, has not been followed in all jurisdictions. Some, in fact, have expressly rejected it. Adding to the confusion is the fact that, regardless of the common law, many jurisdictions have enacted specific legislation or regulation some of which may conflict with applicable federal laws.
And, aside from the confused state of the law, there are the scientific and policy questions of whether a therapist really can predict a patient's behavior and, even if so, whether it is good public policy to have therapists reveal confidential information their patients expected them to keep secret.