Theories of liability
Aider and abettor
“Because a conspirator can be liable for a crime committed by any other conspirator, and the defendant need not do (or even encourage) anything criminal except agree to commit a crime, it is reasonable to make a conspirator not liable for another conspirator's crime that is a fresh and independent product of the mind of one of the confederates outside of, or foreign to, the common design. But aiding and abetting is different. An aider and abettor is someone who, with the necessary mental state, by act or advice aids, promotes, encourages or instigates, the commission of the crime. Because the aider and abettor is furthering the commission, or at least attempted commission, of an actual crime, it is not necessary to add a limitation on the aider and abettor's liability for crimes other principals commit beyond the requirement that they be a natural and probable, i.e., reasonably foreseeable, consequence of the crime aided and abetted. If the prosecution can prove the nontarget crime was a reasonably foreseeable consequence of the crime the defendant intentionally aided and abetted, it should not additionally have to prove the negative fact that the nontarget crime was not committed for a reason independent of the common plan. [¶ ] To be sure, whether an unintended crime was the independent product of the perpetrator's mind outside of, or foreign to, the common design may, if shown by the evidence, become relevant to the question whether that crime was a natural and probable consequence of the target crime. In a given case, a criminal defendant may argue to the jury that the nontarget crime was the perpetrator's independent idea unrelated to the common plan, and thus was not reasonably foreseeable and not a natural and probable consequence of the target crime. But that would be a factual issue for the jury to resolve, not a separate legal requirement.” (People v. Smith, 60 Cal. 4th 603, 616-617, 180 Cal. Rptr. 3d 100, 337 P.3d 1159 (2014) (internal quotes and citations omitted; emphasis in original).)