What is the test for an aider and abettor to be found guilty of a charge of assisting and abetting a crime?

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.] The jury must find 'the intent to encourage and bring about conduct that is criminal, not the specific intent that is an element of the target offense ....' [Citations.]" (People v. Mendoza (1998) 18 Cal.4th 1114, 1122-1123, original italics.)

An aider and abettor's liability for criminal conduct is of two kinds. First, an aider and abettor with the necessary mental state is guilty of the intended crime. Second, under the natural and probable consequences doctrine, an aider and abettor is guilty not only of the intended crime, but also "for any other offense that was a 'natural and probable consequence' of the crime aided and abetted." (People v. Prettyman (1996) 14 Cal.4th 248, 260.) "Thus, for example, if a person aids and abets only an intended assault, but a murder results, that person may be guilty of that murder, even if unintended, if it is a natural and probable consequence of the intended assault. [Citation.]" (People v. McCoy, supra, 25 Cal.4th at p. 1117.)