What is the test for determining whether a defendant is an aider and abettor or a principal?

whether the defendant is an aider and abettor or a principal even when different evidence and facts support such conclusion." ' " (People v. Maury (2003) 30 Cal.4th 342, 423.) " 'It is settled that as long as each juror is convinced beyond a reasonable doubt that defendant is guilty of murder as that offense is defined by statute, it need not decide unanimously by which theory he is guilty. [Citations.] More specifically, the jury need not decide unanimously whether defendant was guilty as the aider and abettor or as the direct perpetrator. . . . [] . . . [] 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. Sometimes, as probably occurred here, the jury simply cannot decide beyond a reasonable doubt exactly who did what. There may be a reasonable doubt that the defendant was the direct perpetrator, and a similar doubt that he was the aider and abettor, but no such doubt that he was one or the other.' " (People v. Jenkins (2000) 22 Cal.4th 900, 1024-1025.)