In what circumstances will expert testimony be admitted in a criminal case?

In People v. Killebrew, supra, 103 Cal.App.4th at pages 656-657, this court examined and identified the following topics upon which expert gang testimony was properly received: (1) the size, composition or existence of a gang; (2) gang turf or territory; (3) an individual defendant's membership in, or association with, a gang; (4) the primary activities of a specific gang; (5) motivation for a particular crime, generally retaliation or intimidation; (6) whether and how a crime was committed to benefit or promote a gang; (7) rivalries between gangs; (8) gang-related tattoos, gang graffiti and hand signs; and (9) gang colors or attire. As we noted, the list was not exhaustive or an exclusive list of all gang topics for which expert opinion may be admitted. (Id. at p. 657.)