B. CHP's Citing of Motorcyclists
The CHP must also comply with the Fourth Amendment when citing motorcyclists for violating the helmet law. Under California law, a traffic citation is considered an "arrest," see Cal. Pen.Code s 853.5 (West Supp.1996), for which an officer must have probable cause. See, e.g., People v. Parnell, 16 Cal.App.4th 862, 875, 20 Cal.Rptr.2d 302, 309 (1993). While Hannigan concedes that probable cause is required to cite a motorcyclist for violating the helmet law, he argues that an officer's knowledge regarding a motorcyclist's actual knowledge about his helmet's non-compliance is irrelevant, and that whether a motorcyclist's lack of knowledge constitutes a defense to a helmet law citation is a question for the factfinder at trial. "
'Probable cause exists when, at the time of arrest, the agents know reasonably trustworthy information sufficient to warrant a prudent person in believing that the accused had committed or was committing an offense.' " Allen v. City of Portland, 73 F.3d 232, 237 (9th Cir.1996) (quoting United States v. Delgadillo-Velasquez, 856 F.2d 1292, 1296 (9th Cir.1988)). "Conclusive evidence of guilt is not necessary to establish probable cause. Mere suspicion, common rumor, or even strong reason to suspect are not enough, however." McKenzie v. Lamb, 738 F.2d 1005, 1008 (9th Cir.1984) (citing Henry v. United States, 361 U.S. 98, 101, 80 S.Ct. 168, 170, 4 L.Ed.2d 134 (1959)). " 'Courts look to the totality of the circumstances known to the officers' in determining whether there is probable cause for an arrest." United States v. Butler, 74 F.3d 916, 920 (9th Cir.1996). As with a determination of reasonable suspicion, courts can take into account "the experience and expertise of law enforcement agents who observed the defendant's activity." United States v. Valencia, 24 F.3d 1106, 1108 (9th Cir.1994).
*11 We concluded above that an officer making an investigatory stop need not have reasonable suspicion that a motorcyclist has actual knowledge of a helmet's non-compliance if other factors, including the appearance of the helmet, are sufficient to establish reasonable suspicion that the helmet law is being violated. The question remains, however, whether an officer must have particularized probable cause to believe that an individual has actual knowledge of a helmet's non-conformity before citing a motorcyclist for violating the helmet law, or whether the officer need only have general probable cause to believe that the helmet law has been violated. Generally, "an officer need not have probable cause for every element of the offense." Gasho v. United States, 39 F.3d 1420, 1428 (9th Cir.1994), cert. denied, --- U.S. ----, 115 S.Ct. 2582, 132 L.Ed.2d 831 (1995). "However, when specific intent is a required element of the offense, the arresting officer must have probable cause for that element in order to reasonably believe that a crime has occurred." Id. [FN7]
Thus, if the requirement that a motorcyclist wearing a helmet that was certified at the time of purchase have actual knowledge of the helmet's non-conformity to violate the helmet law is a specific intent requirement, the CHP must have specific probable cause to believe that a motorcyclist has actual knowledge of a helmet's non-compliance to cite that motorcyclist for violating the helmet law. In Gasho, the owners of an airplane, which had been seized by customs agents, removed the logbook from their airplane without objection from the agents. The agents later arrested the owners when they refused to return the logbook. The owners filed a Bivens action against the agents alleging that they did not have probable cause to arrest the owners of an airplane for either unlawfully "rescuing" property that had been seized by the customs agents or attempting to prevent a seizure of property, crimes that both have specific intent requirements. This court found that the customs agents could not have reasonably believed that the owners had the specific intent to frustrate or prevent a seizure because the owners did not have notice that the logbook had been seized or was about to be seized, due to the agents' original acquiescence to the owners' taking the logbook. Thus, the agents did not have probable cause to arrest the airplane owners. Id. at 1429-32. See also Kennedy v. Los Angeles Police Dept., 901 F.2d 702, 706 (9th Cir.1989) (finding that police did not have probable cause to arrest Kennedy for grand theft after she took possession of her roommate's belongings as security on a debt where "there was no reasonable basis from which anyone could believe that Kennedy had the specific intent permanently to deprive [the roommate] of her property," as is required for a grand theft conviction).
*12 The helmet law, as interpreted by the California courts and correctly articulated by the district court, requires specific intent as one of its elements. A motorcyclist who is wearing a helmet that was certified by the manufacturer at the time of sale must have actual knowledge of the helmet's non-conformity to be guilty of violating the helmet law. Thus, in addition to intending to wear the helmet in question, the motorcyclist must intend to wear a helmet that he knows does not comply with the helmet law. [FN8]
Thus, because a violation of the helmet law requires specific intent on the part of a motorcyclist wearing a helmet that was certified at the time of purchase, the ticketing officer must have probable cause to believe that the specific intent, caused by the motorcyclist's actual knowledge of non-conformity, exists. The district court properly found that the CHP policy and practice for enforcing the helmet law violate the Fourth Amendment rights of the named plaintiffs and others by citing them for violating the helmet law without any regard for whether the motorcyclists have actual knowledge that their helmets, which were apparently certified at the time of purchase, have been shown not to comply with DOT standards. The written CHP policy regarding helmet law enforcement, in effect since the implementation of the helmet law in 1992, does not require the citing officer to make any determination regarding a motorcyclist's knowledge of non-compliance, but rather states that "[o]fficers should use good judgment prior to citing a person(s) who is wearing a nonapproved helmet. The lack of helmet labeling is not a violation, but may be an indication that the helmet is not DOT approved." In a deposition taken in January 1994, after the Buhl opinion but before the Bianco opinion, Commissioner Hannigan indicated that under the policy, an officer has discretion to cite a motorcyclist without regard to that motorcyclist's actual knowledge of a helmet's non-compliance with Standard 218. Dep. of Hannigan, vol. I at 73-75, 90-91 (January 10, 1994). Citation without regard to actual knowledge has continued even after Bianco indicated that such knowledge was required. Lieutenant Michael J. Nivens, the designated helmet law expert for the CHP in this case, stated in his deposition of September 19, 1994 that the CHP had not changed its written policy regarding enforcement of the helmet law since the law's implementation in January 1992. Dep. of Nivens, vol. IV at 615-616 (Sept. 19, 1994). A colloquy between Easyriders' attorney and Lieutenant Nivens demonstrates that CHP does not consider whether a motorcyclist has actual knowledge of a helmet's non- compliance with Standard 218.