What is the test for adequacy of aiding and abetting instruction?

1. Adequacy of Aiding and Abetting Instruction. Defendants claim the trial court erred in failing to instruct the jury that mere presence at the scene of a crime and mere knowledge of the crime do not constitute aiding and abetting. To be liable for a crime as an abettor, the accused must have instigated or advised the commission of the crime or have been present for the purpose of assisting the crime. He must share the criminal intent with which the crime was committed. Neither his mere presence at the scene of the crime nor his failure, through fear, to prevent a crime [222 Cal.App.3d 557] establishes, without more, that an accused was an abettor. (People v. Durham (1969) 70 Cal.2d 171, 181, 74 Cal.Rptr. 262, 449 P.2d 198.)