What is the test for a charge of aiding and abetting murder?

Murder is the unlawful killing of a human being with malice aforethought ( 187). In order to prove attempted murder, the prosecution is required to establish that the defendant engaged in a direct but ineffectual act towards the killing of another human being and committed the act with the specific intent to kill another human being unlawfully. (People v. Herrera (1999) 70 Cal.App.4th 1456, 1467.)

"All persons concerned in the commission of a crime, whether it be felony or misdemeanor, and whether they directly commit the act constituting the offense, or aid and abet in its commission... are principals in any crime so committed." ( 31.) A person is liable for aiding and abetting when, (1) with knowledge of the unlawful purpose of the perpetrator and (2) with the intent or purpose of committing, or encouraging, or facilitating the commission of the crime, that person (3) by act or advice aids, promotes, encourages, or instigates the commission of the crime. (People v. Gibson (2001) 90 Cal.App.4th 371, 386.)