In People v. Killebrew (2002) 103 Cal.App.4th 644, East Side Crips shot up a Country Boy Crips gathering, killing at least two people. Anticipating retaliation, the Bakersfield police instituted a heightened state of alert. Several hours later, two patrol officers observed three cars apparently traveling together in East Side Crip territory. In each of the first two vehicles - a Chevrolet and a Mazda - they saw four young Black males. In the third car, a Chrysler, the officers saw two young Black males and either one or two passengers in the back seat. Of all the men, the officers recognized only one - Leon Anderson - and they knew him to be a member of the East Side Crips. Because the cars carried young Black males, appeared to be traveling together, and one passenger was an East Side Crip, the officers concluded that everyone in the vehicles was a member of the gang. They further reasoned that because the gang would be expecting retaliation, they would travel only in large groups that night and would carry weapons for protection. Accordingly, they initiated a stop of the Chevrolet, in which Anderson was riding. As they approached, they saw the rear seat passenger place a handgun under the front seat. Officers arrested the four occupants of the vehicle and recovered the handgun. Meanwhile, the other two vehicles made a U-turn and drove by the location of the stop; other officers were dispatched and found these vehicles at a nearby taco stand. A search of the area revealed a handgun hidden in a shoe box next to a Dumpster. All seven occupants of the vehicles were arrested. Killebrew was not in the Chevrolet or the Mazda, and his presence in the Chrysler was not established with any degree of certainty. He was seen observing the stop of the Chevrolet, however, and was arrested and charged with conspiring to possess the two handguns. At trial, a police officer testified as an expert on gangs to establish not only Killebrew's membership in a criminal street gang, but also his subjective knowledge and intent to possess the handgun. Killebrew was ultimately convicted of conspiring to possess a handgun. (Killebrew, supra, 103 Cal.App.4th at pp. 647-649.) On appeal, Killebrew argued, inter alia, that the trial court erred by allowing Officer Darbee, the gang expert, to give an opinion about the intent and knowledge of gang members when in the presence of guns. (Killebrew, supra, 103 Cal.App.4th at pp. 649-650.) In this respect, Darbee testified at length about gangs and gang psychology; he identified the major gangs in the Bakersfield area and testified about the major criminal activities of the East Side Crips; and he opined that the individuals involved in this case were all members of the East Side Crips and that they would have expected the Country Boy Crips to retaliate as a result of the shooting. Killebrew did not claim these opinions were inadmissible, but instead took issue with the trial court's admission of Darbee's testimony concerning the subjective knowledge and intent of each occupant in the car. In this respect, Darbee testified that when one gang member in a car possesses a gun, every other gang member in the car knows of the gun and constructively possesses it. Darbee went so far as to opine that the occupants of the Chrysler, to which no gun was ever linked, would know of the guns in the other two vehicles and would mutually possess those guns. (Id. at p. 652 & fn. 7.) The Court undertook an extensive review of cases addressing the propriety of expert testimony on gangs (Killebrew, supra, 103 Cal.App.4th at pp. 652-657), and noted that Darbee's testimony was not the type of "culture and habit testimony" found in the various reported cases. (Id. at p. 654.) The Court stated: "None of the cases reviewed permitted testimony that a specific individual had specific knowledge or possessed a specific intent. People v. Olguin (1994) 31 Cal.App.4th 1355 came close to addressing this issue when the appellate court held the officer's testimony was admissible since it was framed in terms of gangs in general, not a specific defendant's subjective expectation. "The testimony to which the defendant objected was: '"Q. Now, do you have an opinion as to a gang member's expectation of what will result from, let's say, a mutual yelling out of gang names or affiliations" A. Yes. Q. And what is that opinion? A. The gang member would expect a violent confrontation."' " "Darbee's testimony went must further than the officer's testimony in Olguin did. Through the use of hypothetical questions, Darbee testified that each of the individuals in the three cars (1) knew there was a gun in the Chevrolet and a gun in the Mazda, and (2) jointly possessed the gun with every other person in all three cars for their mutual protection. In other words, Darbee testified to the subjective knowledge and intent of each occupant in each vehicle. Such testimony is much different from the expectations of gang members in general when confronted with a specific action. "Darbee's testimony was the only evidence offered by the People to establish the elements of the crime. As such, it is the type of opinion that did nothing more than inform the jury how Darbee believed the case should be decided. It was an improper opinion on the ultimate issue and should have been excluded. "Moreover, this topic is not one for which expert testimony is necessary. Testimony that a gang would expect retaliation as a result of a shooting such as occurred in the case, that gangs would travel in large groups if expecting trouble, that in a confrontation more than one gang member may share a gun in some identified circumstances, and that oftentimes gang members traveling together may know if one of their group is armed, would have been admissible. Beyond that, Darbee simply informed the jury of his belief of the suspects' knowledge and intent on the night in question, issues properly reserved to the trier of fact. Darbee's believes were irrelevant.... Since the erroneously admitted testimony provided the only evidence to support the conspiracy theory, reversal of the judgment is required." (Killebrew, supra, at pp. 658-659.)