What is the test for a jury to convict a defendant as an accomplice to an intentional killing?

However, to reach a true finding on the witness-killing special circumstance, the jury necessarily found either that defendant alone committed the intentional murder or that he aided and abetted the actual perpetrator of the intentional murder. For the purpose of our analysis we must assume the latter. As a result, as with the felony-murder verdicts (ante, at pp. 271-273 of 254 Cal.Rptr., at pp. 433-434 of 765 P.2d), we are again faced with the inadequacy of the aiding and abetting instruction (People v. Beeman, supra, 35 Cal.3d 547, 199 Cal.Rptr. 60, 674 P.2d 1318), and we again apply the Chapman test to determine the prejudicial effect of the Beeman error. (People v. Dyer, supra, 45 Cal.3d 26, 246 Cal.Rptr. 209, 753 P.2d 1.)

In convicting the defendant as an accomplice to an intentional killing, the jury must necessarily have found that he committed the "aiding" act and that he did so with knowledge of the perpetrator's criminal purpose, i.e., to kill for the purpose of preventing the victim's testimony. Because of the manner in which defendant defended the case--denial that he in any way aided in the killing--there is no way for the jury to find that he "aided" the killing only "accidentally" or "unintentionally." (See People v. Beeman, supra, 35 Cal.3d at p. 560, 199 Cal.Rptr. 60, 674 P.2d 1318.)