A murder case that had some features in common with the Tarasoff case occurred in Sasebo City, Japan, in 2014. A 15-year-old high school girl was murdered and her 16-year-old classmate was arrested on suspicion of homicide. One and a half months before the murder, a psychiatrist who had been examining the girl called a prefectural child consultation centre to warn that she might commit murder, but he did not reveal her name, considering it his professional duty to keep it confidential. Article 134 of the Japanese Criminal Law states that doctors should not disclose patient information obtained in clinical practice without a legitimate reason, but the Japanese Supreme Court has not specified what constitutes a legitimate reason. Mass media and commentators suggested that the murder could have been prevented if the psychiatrist had disclosed the girl's name to the authorities or had isolated her coercively in a psychiatric ward. However, the authors disagree with such claims. This article discusses obligations imposed on concerned individuals and third party members in cases involving ethical dilemmas regarding patient confidentiality and information disclosure. It is concluded that everyone should fulfill their obligations to prevent such tragedies and one should judge the appropriateness of others’ actions based not on the consequences of their actions, but on the processes used to decide on a course of action and their commitment. It is necessary for us to establish a society in which concerned parties can do what they think is ethically best without fearing ungrounded charges.