What are the legal principles of aiding and abetting in a murder case?

"A court must instruct sua sponte on genera] principles of law that are closely and openly connected with the facts presented at trial. [Citations.]" (People v. Ervin (2000) 22 Cal.4th 48, 90, 91 Cal. Rptr.2d 623, 990 P.2d 506.) Of course, there was no suggestion that defendant was a mere aider and abettor; it was the prosecution's theoryand the evidence showedthat defendant was the one who personally fired the gun, killing the victim. Moreover, P.M. had been granted immunity and was not on trial. It would thus appear aiding and abetting instructions were unnecessary.