In what circumstances will a police officer be found liable for causing emotional distress to a witness in harm's way?

In this context, "in harm's way" refers to harm from some other source, not harm inflicted by the police officer. (See Bastian v. County of San Luis Obispo (1988) 199 Cal.App.3d 520, 529; see, e.g., Carpenter v. City of Los Angeles (1991) 230 Cal.App.3d 923, 931-932 [police created special relationship with witness to crime by assuring him that he was in no danger and by failing to warn him of threats against him].) This follows from the fact that a special relationship is an exception to the public duty rule; hence, it gives rise to a duty to protect. If a special relationship arose every time a police officer personally inflicted emotional distress, that would make the general rule that there is no duty to avoid negligently causing emotional distress inapplicable to police officers; the special relationship exception would always apply.