What is the test for an accomplice to be held liable in a robbery case?

Robbery, the underlying felony offense charged in this case, is "the felonious taking of personal property in the possession of another, from his person or immediate presence, and against his will, accomplished by means of force or fear." ( 211.) Also relevant, "an accomplice is liable for killings occurring while the killer was acting in furtherance of a criminal purpose common to himself and the accomplice, or while the killer and the accomplice were jointly engaged in the felonious enterprise. [Citation.] In order to support defendant's conviction as an aider and abettor [of felony murder], therefore, the record must contain substantial evidence that (a) [the perpetrator] committed the robbery [to wit, the felony offense] (the perpetrator's actus reus), (b) defendant knew [the perpetrator's] intent to rob [to wit, to commit the felony] and intended to assist in the [commission of the felony] (the aider and abettor's mens rea), and (c) defendant engaged in acts that assisted the [felony] (the aider and abettor's actus reus)." (People v. Thompson (2010) 49 Cal.4th 79, 117.)