The Supreme Court recently gave prosecutors a green light to prove defendants' criminal intent vicariously, by offering expert testimony about the mental state of people "like" the defendant.

At the tail end of its recent term, the court held in Diaz v. United States that while Rule 704(b) of the Federal Rules of Evidence prohibits an expert from testifying that a particular defendant had a culpable state of mind when engaged in allegedly criminal conduct, that rule does not bar an expert from testifying that "most people" have a guilty mental state when they engage in the same activity.

"The upshot," observed the dissenting justices, is that "[p]rosecutors can now put an expert on the stand—someone who apparently has the convenient ability to read minds—and let him hold forth on what 'most' people like the defendant think when they commit a legally proscribed act. Then, the government need do no more than urge the jury to find that the defendant is like 'most' people and convict." In so holding, Diaz put "a powerful new tool in the government's pocket."