What is the test for aiding and abetting murder?

In order to prove a defendant guilty based upon a theory of aiding and abetting, the prosecution must prove all of the following beyond a reasonable doubt: that (1) the perpetrator committed a crime; (2) the aider and abettor knew of the perpetrator's unlawful purpose; (3) the aider and abettor intended to assist the perpetrator in achieving his unlawful purpose; and (4) the aider and abettor, by his conduct, assisted in or facilitated commission of the crime. (People v. Thompson (2010) 49 Cal.4th 79, 116-117.)

Murder is the unlawful killing of a human being with malice aforethought. ( 187.) Malice may be express or implied. ( 188.) Express malice is an intent to kill while implied malice is the doing of an intentional act, the natural consequences of which are dangerous to human life, with knowledge of the danger to, and with conscious disregard for, human life. (People v. Swain (1996) 12 Cal.4th 593, 600-601.)

Murder which is willful, deliberate, and premeditated is murder of the first degree. (People v. Swain, supra, 12 Cal.4th at p. 601; see also 188.) Second degree murder includes unpremeditated express malice murder as well as all implied malice murder. (People v. Swain, at p. 601; see also 188.)