When Is Following Someone to Investigate Their Possible Misconduct a Crime?

Compare Anonymous v. Anonymous (N.Y. Sup. Ct. 2010) and Fisher v. Johnson, 1992 WL 83309 (Minn. Ct. App. Apr. 28). Anonymous concludes that “hiring of a professional, licensed private investigator in a matrimonial action to gather evidence [of a spouse’s infidelity] is for a proper and legitimate purpose,” and doesn’t constitute criminal harassment, criminal stalking, or conduct that justifies the issuance of a restraining order. (Let’s focus here on conduct that consists just of following and photography, and doesn’t include breaking into people’s homes, tapping their phone lines, hacking their computers, pretending to be someone else in order to get confidential information from banks or phone companies, or other conduct that is independently criminal.)

Fisher, on the other hand, upholds a restraining order against a mother who was following her daughter, “presumably to gather evidence of alcohol use in an effort to win custody of one or all of Fisher’s children.” Such conduct, the court held, was an “intentional violation of privacy” and a violation of the state statute, which justified the issuance of a restraining order that would prevent future such behavior. Nothing in the opinion suggested that plaintiff reasonably feared a violent attack from her mother (though there had been “alleg[ations of] various violent confrontations,” it was the invasion of privacy and not any threat that was the basis for the decision).

Let’s assume that both decisions are consistent with the relevant state statutes (which are worded differently). My question: What should be the proper rule in cases such as this? One can imagine a wide range of other such situations as well, such as a father having his child’s lover followed to see whether the lover is lying about various things, an investigative reporter following someone who he suspects is engaged in some sort of fraud, a lawyer hiring a private investigator to follow a client’s adversary to see whether the adversary is lying about being badly injured, and so on?

Again, please assume that all we have is following (perhaps coupled with asking questions of motel clerks, bartenders, and so on), not break-ins and the like, and that the following is not seen as threatening violence, either because the target was unaware that he or she was being followed, or because the target knows the follower and recognizes that the follower is looking for information, not an opportunity for an attack.