The case is Rich v. Fox News, issued on September 13. This case involves traditional tort theories: Intentional Infliction of Emotional Distress and Tortious Interference with Contract. These are state law principles that sometimes wind up in federal court. Intentional Infliction claims are difficult to win, and the New York Court of Appeals has never sustained such a claim, though other courts have done so. You have to prove the defendant did something so outrageous and beyond the pale that it foreseeably caused you to suffer emotional distress. This high standard ensures that most personality disputes and conflicts do not find their way into court. As for the contract claim, it's as it sounds: you cannot interfere with the contractual relationship between other people.
The Court of Appeals (Calabresi, Droney and Underhill [D.J.], summarizes the allegations, and they are not pleasant:
Malia Zimmerman (a Fox News reporter) and Ed Butowsky (a Fox News commentator) allegedly set out “to take the conspiracy theory from the fringe to the front pages and screens of the mainstream media.” Over the course of several months, Zimmerman and Butowsky recruited a Fox News contributor, Rod Wheeler, to help them infiltrate the Rich family. They convinced the Plaintiffs, Seth’s parents, to hire Wheeler as a private investigator to look into the circumstances of Seth’s death. And they then exploited Wheeler’s connection to the Riches to give credence to what Zimmerman and Butowsky knew were false accusations against Seth—which Zimmerman and Butowsky widely disseminated through Fox News. They did this, it is claimed, with full knowledge of the harm it would do to Seth’s parents.If you do this to someone, you will get sued for IIED, as they call the Intentional Infliction cases. Judge Calabresi, an expert on American tort law, says that while IIED cases are hard to prove, "We have no trouble concluding that -- taking their allegations as true -- the Riches plausibly alleged what amounted to a campaign of emotional torture" but setting up the Riches with an "investigator" who would win their trust and allow them to advance the false story that Seth Rich was in contact with Wikileaks and that he leaked the emails himself.
As for the contractual inference claim, the Riches did sign a contract with the investigator. The investigator breached that contract in violating confidentiality with his clients. Plaintiffs allege that the breach happened because of Fox News's interference as a means to advance the false story about Seth Rich. So what we have is traditional tort theories for the modern age. Judge Calabresi would tell you that American tort law is timeless, crafted and molded by judges over the course of more than 100 years to deal with the multitude of situations that cause harm and require that someone be held responsible for that harm. These doctrines are taught in first-year law school as a means to emphasize the basic principle that if you do something negligently or intentionally and hurt someone in the process, you can be responsible for their damages. Calabresi, the former Dean of Yale Law School teachers these principles to Fox News.