When can a defendant request disclosure on the theory that an informant could be a material witness on the issue of guilt?

However, appellant's request for disclosure on the theory that the informant could be a material witness on guilt entails a different analysis. When a defendant demands disclosure "on the ground the informant is a material witness on the issue of guilt, the court shall conduct a hearing at which all parties may present evidence on the issue of disclosure." (Evid. Code, 1042, subd. (d). "An informant is a material witness if there appears, from the evidence presented, a reasonable possibility that he or she could give evidence on the issue of guilt that might exonerate the defendant. [Citation.] The defendant bears the burden of adducing ' " 'some evidence' " ' " on this score. (People v. Lawley (2002) 27 Cal.4th 102, 159.)