In a criminal case, in what circumstances will the court refuse an instruction from a witness that he or she was an accomplice?

In a criminal case, even in the absence of a request, the trial court must instruct the jury on all general principles of law relevant to the issues raised by the evidence. (People v. Hovarter (2008) 44 Cal.4th 983, 1021; People v. Abilez (2007) 41 Cal.4th 472, 517.) The court may, however, properly refuse an instruction if it is not supported by substantial evidence. (Hovarter, supra, at p. 1021.)

When there is sufficient evidence that a witness is an accomplice, the trial court must sua sponte instruct the jury both on the principals of accomplice testimony as well as the need for corroboration of accomplice testimony. (People v. Tobias (2001) 25 Cal.4th 327, 331; see also People v. Zapien (1993) 4 Cal.4th 929, 981-982.) Section 1111 defines an accomplice as "one who is liable to prosecution for the identical offense charged against the defendant on trial in the cause in which the testimony of the accomplice is given." A person is liable to be prosecuted for an identical offense when he or she is a principal. Section 31 defines a principal as anyone who is "concerned in the commission of a crime... whether they directly commit the act constituting the

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