In an unannounced memorandum, U.S. Attorney General William Barr informed all U.S. attorneys that he’s established a “national disruption and early engagement program” that will identify mass shooters before they commit a crime.

Promising to “identify, assess, and engage potential mass shooters before they strike,” Barr committed the “full attention of the U.S. government” to “preventing these types of attacks.”

This program is nothing more or less than a pre-crime unit, tasked with scouring the data collected by the many federal agencies that keep every American under constant surveillance.

Barr promises his underlings that together they will work “shoulder to shoulder” to “disrupt individuals who are mobilizing toward violence.”

There are several legal and constitutional impediments to AG Barr’s planned pre-crime program.

First, in the United States, a person cannot be charged and tried for a crime unless mens rea and actus rea are established as facts.

Mens rea and actus rea are critical elements of criminal law that have existed for centuries in American and English law. The terms are taken from the Latin maxim: ‘Actus non facit reum nisi mens sit rea’ (a person is not guilty of an act unless his mind is also guilty).

Put simply, mens rea means a guilty thought (an intent to do something), and the actus rea is the act itself.

The relationship of these two aspects of criminal behavior are summarized succinctly by attorney Jordan Rickards:

In any criminal case, the action, as well as the intention, must be established for a person to be charged with a crime. The degree and the kind of causation must also be considered. Also, all legitimate defenses, mitigating factors, and extenuating circumstances must be taken into account for a criminal charge to be determined.

The principles of mens rea and actus rea are part of the Modal Penal Code (MPC), which was developed by the American Law Institute in 1962. The modal law represents a seminal work that has greatly influenced criminal law in the US.

In light of this legal reality, William Barr’s proposed pre-crime program is prima facie a violation of one of the most sacrosanct Anglo-American legal maxims.