Judges in federal criminal cases provide juries with instructions before the jury members retire to consider their verdict. In some situations, the judge may include alternative theories of guilt, informing the jury that it may convict a defendant of a single offense on the basis of one of several different theories. But because most juries in federal criminal trials deliver only a general verdict of either “guilty” or “not guilty,” it is usually not possible to determine the theory upon which the jury relied in reaching its decision. This lack of transparency may be problematic if the defendant appeals his conviction on the basis of an alleged “alternative theory error,” which occurs when one—but not all—of the theories in the jury instruc...