The Germanwings Flight 9525 tragedy is raising questions about whether psychiatrists should tell the authorities about patients with troubled minds who have the lives of the public in their hands.
What you say to your doctor is usually confidential. But 45 states have laws requiring or permitting mental health professionals to disclose if they believe a patient is dangerous.
"There's legal and there's ethics, so legally right now I'm under no obligation as a physician to tell anyone," says Dr. Robert Klitzman, a professor of psychiatry at Columbia University.
"Ethically, however, I would argue that if I'm a physician, and I know someone may have a plane full of people and crash it, I feel that there may be times when I have an obligation to notify someone," Klitzman says.
A case from 40 years ago shows the danger of a doctor keeping quiet.
In 1969, California college student Prosenjit Poddar killed a woman he'd met in a dance class. Before the murder, Poddar told his therapist about his desire to kill Tatiana Tarasoff. The therapist didn't warn the victim.
"And a court found that he [the therapist] was liable, that in that case, he should have violated patient confidentiality," Klitzman says. "So there's an ethical standard on the one hand, and a legal standard on the other."
But even reporting is not foolproof.
After James Holmes shot and killed 12 people at an Aurora, Colorado, movie theater in 2012, the investigation revealed his psychiatrist had warned police that Holmes was dangerous and homicidal. It's not clear if anything was done.
Some privacy advocates agree that there are cases where warning law enforcement is necessary -- but they worry about a chilling effect on patients.
"You might deter people from seeking mental health services in order to avoid disclosing things they want to keep private," says Chad Marlow of the American Civil Liberties Union.
Here in the U.S., the Federal Aviation Administration mandates that airline pilots self-report mental health issues. The agency says it's too early to discuss whether the protocols will be strengthened.