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Facebook wants law enforcement to get off its lawn. Last September, its director and associate general counsel Andrea Kirkpatrick sent a letter to Memphis police chastising the department for violating the social media platform's policies by engaging in “inauthentic behavior.”

The platform specifically takes issue with the department and other law enforcement agencies creating fake profiles, claiming that the practice violates the trusting and authentic environment the platform is trying to create. The courts, however, haven't given police much reason to comply.

“Look, Facebook can have it's own rules and then if they catch the police, they throw them off Facebook, right? But that's different than would a court say you broke the law by doing this,” Jules Epstein, a professor and director of advocacy programs and clinical legal education at Temple University, said.

A decision rendered earlier this year by the Supreme Court of Delaware in the case of Everett v. State of Delaware ruled that the risk of being betrayed by an informer or deceived as to someone's identity “is probably inherent in the conditions of human society and is the kind of risk necessarily assumed whenever people speak.” In other words, the Fourth Amendment protects against illegal search and seizure, not mistaken trust.

“I think as a general rule that if you invite people onto something, it's at your risk.” Epstein said.

In Everett an undercover police officer used an illegitimate account to befriend and keep tabs on the defendant up to three times a week for two years. When the defendant, who was prohibited from possessing a firearm, posted a photo of his nightstand on which a gun was clearly visible, it became the basis for a warrant to search Everett's house.

The defendant tried to have the evidence attained from that search suppressed on the basis of the Fourth Amendment, arguing that if the magistrate knew the officer had obtained the photo using a phony Facebook account, the judge may not have found probable cause.

The court ruled that a Fourth Amendment violation could not exist where there was no reasonable expectation of privacy.

“If you leave your diary open on a picnic table in a park and I lean over and start reading it, even if I'm a police officer and I have no legal reason to do it, it's not a search because there's not what is called 'an expectation of privacy' for something you've left out in the open,” Epstein said.

Determining what constitutes “reasonable” or “privacy” can be dicey, especially when it comes to social media. After all, diaries don't generally come with privacy settings. In the case of the United States v. Meregildo, an opinion by a district court in New York reasoned that Facebook postings made using secure privacy settings “reflect the user's intent to preserve information as private and may be constitutionally protected.”

In that instance, police might be forced to appeal to Facebook directly or obtain a warrant. However, the protection ends the moment an account holder adjusts settings to allow posts to be viewed by friends.

In Meregildo, the government was given access to defendant Melvin Colon's Facebook page by a “friend” of the account turned informant, and used the evidence gathered there as probable cause to support an application for a search warrant.

Again, the same reasoning that formed the basis for the decision in Everett was applied. The  New York court noted that even if the defendant had not mistakenly placed his trust in the undercover cop, one of his other Facebook friends could have seen the photo of the gun and reported it to the police anyway.

“If one allows others to have access to his or her information that contains evidence of criminal wrongdoing, then that person assumes the risk that they might expose that information to law enforcement, or they might be undercover officers themselves,” the decision reads.