In what circumstances will a jury be required to agree unanimously on a single charge of assault or attempted murder?

appropriate 'when conviction on a single count could be based on two or more discrete criminal events,' but not 'where multiple theories or acts may form the basis of a guilty verdict on one discrete criminal event.' [Citation.] In deciding whether to give the instruction, the trial court must ask whether (1) there is a risk the jury may divide on two discrete crimes and not agree on any particular crime, or (2) the evidence merely presents the possibility the jury may divide, or be uncertain, as to the exact way the defendant is guilty of a single discrete crime. In the first situation, but not the second, it should give the unanimity instruction." (People v. Russo (2001) 25 Cal.4th 1124, 1134-1135.)

This case presents the second situation because the prosecutor properly proceeded on multiple theories: defendant was the actual perpetrator of the assault and attempted murder and defendant was liable for those offenses on an aiding and abetting theory. In this situation, the jurors need not unanimously agree "'whether the defendant is an aider and abettor or a principal even when different evidence and facts support each conclusion.' [Citations.]" (People v. Jenkins (2000) 22 Cal.4th 900, 1026.) In other words, "as long as each juror is convinced beyond a reasonable doubt that defendant is guilty of [the charged crime] as that offense is defined by statute, it need not decide unanimously by which theory he is guilty. [Citations.] . . . [] Not only is there no unanimity requirement as to the theory of guilt, the individual jurors themselves need not choose among the theories, so long as each is convinced of guilt." (People v. Santamaria (1994) 8 Cal.4th 903, 918-919.) It therefore follows that the trial court was not required to instruct the jury that in order to find defendant guilty of either assault or attempted murder, it must agree upon the act constituting each crime.