Tatiana Tarasoff and Prosenjit Poddar were both students at the University of California at Berkeley when they met for the first time at a folk dancing class in 1968. He was a 26-year old graduate student in Naval Architecture who had grown up in India as part of the untouchable Dalit caste and had little experience with dating or American customs. She was an undergraduate and, while they dated on several occasions, did not view the relationship as a serious one. Poddar grew infuriated with her attempts at breaking off their relationship to be with other men and became obsessed with her. In his attempts at rekindling their relationship, he became despondent, neglected his studies, was often seen weeping, and generally began acting in a bizarre fashion. He spoke with a friend about blowing up her dormitory room and was advised to seek counseling at the University Health Service.
While Tatiana went to Brazil to spend the summer with an aunt, Poddar attended therapy with a staff psychologist, Dr. Lawrence Moore. Over the course of the treatment sessions, he indicated violent fantasies towards Tatiana including getting a gun and shooting her (while he never named her in the sessions, she was easily identified). Due to concerns about Poddar, Dr. Moore notified campus police who picked him up but later released him after he promised to stay away from Tatiana. Dr. Moore's supervisor, Dr. Harvey Powelson, instructed staff to refrain from making further attempts at hospitalizing Poddar. Poddar never returned to therapy and neither Tatiana nor her parents received any warning that Poddar was a potential threat.
In the weeks prior to Tatiana's return from Brazil, Poddar moved in with her brother who had no idea that he intended any harm to his sister. On October 27, 1969, shortly after her return, Poddar went to her house and stabbed her to death with a kitchen knife. He then called the police and asked to be handcuffed.
Tatiana's parents filed lawsuits against the campus police, the health service, and the Regents of the University of California for failing to provide proper warning. The first trial was dismissed on the grounds that there was no cause for action as the therapist's primary responsibility was to the patient rather than a third party. After the Appeals Court supported this decision, the case was taken to the California Supreme Court.
It was in 1974 that the Tarasoff Decision was first handed down. In this landmark decision, the Court ruled that the therapist bears a duty of reasonable care to give threatened persons such warning as to avert foreseeable danger arising from the patient's mental state. Since this decision now meant that police and mental health professionals were obligated to warn potential victims, the case was reheard by the California Supreme Court in 1976. The revised decision held that, while police could not be held liable, health professionals were obliged to warn potential victims because of the "special relationship between a patient and his doctor or psychotherapist". In an often-quoted statement by Justice Matthew Tobriner presenting the majority opinion: ""... the confidential character of patient-psychotherapist communications must yield to the extent that disclosure is essential to avert danger to others. The protective privilege ends where the public peril begins."
Since 1976, the Tarasoff decision has been challenged in numerous legal settings and has been upheld in at least 17 U.S. states (the states of Florida, Texas, South Carolina, and Virginia have rejected the decision). Later decisions have limited the scope of the Tarasoff Decision to only provide a duty to warn identifiable victims, i.e., potential victims who could be readily identified based on information provided by the patient. The Tarasoff has been highly influential in non-U.S. jurisdictions as well (here in Canada, psychotherapists are encouraged to follow the Tarasoff provisions even though it has no formal weight in Canadian law).
As for Prosenjit Poddar, he served four years out of a five-year sentence for manslaughter which was subsequently overturned on a technicality relating to improper jury instructions on diminished capacity. To avoid a new trial, Poddar agreed to return to India. Based on available reports, he is now happily married.