In determining whether to give requested instructions on third party culpability, courts often rely on the language in People v. Hall (1986) 41 Cal.3d 826, 833:

"To be admissible, the third-party evidence need not show 'substantial proof of a probability' that the third person committed the act; it need only be capable of raising a reasonable doubt of defendant's guilt. At the same time, we do not require that any evidence, however remote, must be admitted to show a third party's possible culpability. . . . Evidence of mere motive or opportunity to commit the crime in another person, without more, will not suffice to raise a reasonable doubt about a defendant's guilt: there must be direct or circumstantial evidence linking the third person to the actual perpetration of the crime."