In what circumstances will a jury be instructed to convict a defendant of aiding and abetting?

In deciding to instruct the jury on aiding and abetting, the court stated: "The thing that sways me is the fact that the physical evidence shows there were two guns used, and there's no getting around that issue." Appellant essentially argues that this evidence was insufficient to support giving the instructions because the trial court ignored other plausible scenarios explaining the presence of two different caliber shell casings found in the driveway. But the existence of other possible theories does not mean that the physical evidence at hand was insufficient to support the prosecution's theory of aiding and abetting. (See People v. Alexander (2010) 49 Cal.4th 846, 921 ["Because the evidence could support aiding and abetting liability, the trial court properly gave the aiding and abetting instructions"].)