Two weeks ago the FBI arrested Paul Kevin Curtis for sending letters laced with ricin to President Obama and Senator Wicker of Mississippi, and it has been another week since the charges were dropped. Now the FBI has a second suspect in custody who may be responsible for sending the letters.

One lesson to be learned from the episode is the importance of letting the judicial process take its course and realizing that it is not just a cliche that a person is innocent until proven guilty. It is a central concept of our judicial system that until a person is convicted, they are still innocent under the law, and travesties will happen if we let mob mentality undermine that.

However, the episode also shows the depressingly low standard that it takes to arrest someone or for a judge to issue a search warrant. The Supreme Court has said that the standard for both an arrest and a search warrant is “probable cause.” The definition of probable cause has evolved a bit, but we are now using the definition outlined in a 1983 case, Illinois v. Gates, in which the Court said, “probable cause does not demand the certainty we associate with formal trials.” Instead, judges issuing search warrants should determine whether “there is a fair probability that contraband or evidence of a crime will be found in a particular place…. This flexible, easily applied standard will better achieve the accommodation of public and private interests.”

The Court is correct that this is an easily applied standard. It is easily applied because it sets the bar so low. The Court has never set a numerical value on what “fair probability” means, but if I were to say there is a fair probability of rain tonight, and the weatherman says there is a 15% of rain tonight, I don’t think anyone would find those statements contradictory. As has become apparent in the 30 years since the Gates decision, judges have interpreted “fair probability” to mean “within the realm of possibility.”

It is doubtful the FBI will voluntarily release the information that backed their search warrant and arrest of Paul Kevin Curtis, but from news reports, it appears there was little evidence against him. Both letters were signed “I am KC and I approve this message.” That is a sign off phrase Curtis has used in internet postings. The FBI acknowledged that the letters and stamps had no fingerprints and were sealed with self adhesives, leaving no DNA evidence. It would seem that the “probable cause” leading to the arrest and search of Mr. Curtis’ house consisted entirely of the repetition of phrases that he likes to use in social media, and the fact that he lives in Mississippi and his initials are KC.

If that is all it takes to establish probable cause, there is not much stopping the police from searching anyone’s home and not much stopping them from arresting just about anyone.