What is the test for an aider and abettor to be found guilty of a charge of accessory to murder?

"The actual perpetrator must have whatever mental state is required for each crime charged . . . . An aider and abettor, on the other hand, must `act with knowledge of the criminal purpose of the perpetrator and with an intent or purpose either of committing, or of encouraging or facilitating commission of, the offense.' [Citation.] . . . Once the necessary mental state is established, the aider and abettor is guilty not only of the intended, or target, offense, but also of any other crime the direct perpetrator actually commits that is a natural and probable consequence of the target offense. [Citation.]" (People v. Mendoza (1998) 18 Cal.4th 1114, 1123, first italics in original, second italics added.)