Is there any case law that supports the argument that a person's right to privacy is violated by the police?

accused is not a passive victim of government intrusion; "rather ... by taking a companion into his confidence, [the accused has] in essence extended his zone of privacy to embrace the companion as to any confidences so disclosed. There is simply no constitutional principle that prohibits the recipient of a confidence from breaching the trust reposed in him not to disclose it to others, including the police." ( People v. Phillips (1985) 41 Cal.3d 29, 53, 222 Cal.Rptr. 127, 711 P.2d 423.)