What is the test for an aider and abettor to be found guilty of a homicide-related crime?

One who aids and abets an offense is guilty as a principal. ( 31.) To be guilty as an aider and abettor, a person 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. [Citations.]" (People v. Beeman (1984) 35 Cal.3d 547, 560, italics omitted.) "The liability of an aider and abettor extends also to the natural and probable consequence of the acts he knowingly and intentionally aids and encourages. [Citation.]" (Id. at p. 560.)

An aider and abettor may be found guilty of a greater homicide-related offense than the actual perpetrator: "[W]hen a person, with the mental state necessary for an aider and abettor, helps or induces another to kill, that person's guilt is determined by the combined acts of all the participants as well as that person's own mens rea. If [the aider and abettor's] mens rea is more culpable than another's, that person's guilt may be greater even if the other might be deemed the actual perpetrator." (People v. McCoy (2001) 25 Cal.4th 1111, 1122.) Likewise, an aider and abettor can be convicted of a lesser homicide-related offense than the actual perpetrator. (See People v. Samaniego (2009) 172 Cal.App.4th 1148, 1164-1165.)

Generally, "the extent of an aider and abettor's liability is dependent upon his particular mental state, which may, under the specific facts of any given case, be the same as, or greater or lesser than, that of the direct perpetrator." (People v. Mejia (2012) 211 Cal.App.4th 586, 624.)