In Sanders v. City of Philadelphia, 209 F. Supp. 2d 439 (E.D. Pa. 2002), a civil suit for, inter alia, unlawful detention and false arrest, the court concluded that there was probable cause to arrest the passenger as a matter of law.
In that case, the police officer noticed an automobile engaged in erratic maneuvers. Subsequently, the officer received confirmation that the vehicle had been reported stolen.
After pulling the vehicle over, he found two people inside -- the driver and the plaintiff. Both were arrested, but the charges against the plaintiff were later dismissed, and she brought suit alleging that the officer lacked probable cause when detaining and ultimately arresting her.
The court entered summary judgment in favor of the defendants on all federal and state false arrest and unlawful detention claims, stating:
While it is true the plaintiff was not operating the automobile, a prudent person is perfectly justified in believing that a passenger is somehow involved in the theft whether it be as an accomplice, conspirator or primary suspect. Sanders' apparent voluntary presence in a stolen automobile gives sufficient probable cause to warrant arrest and further investigation by the police.
When balancing the interests of the individual riding in a stolen car against those of society it is clear that the interests of society prevail. A finding of no probable cause forces police to allow potential criminals in such a situation to go free only to be able to hinder society again by repeating the crime. On the other hand, a finding of probable cause allows the police to detain the occupant of a stolen car long enough to find out what involvement, if any, the suspect had in the theft itself. The decision here is an easy one. The interests of society must prevail in this situation. The burden to the individual who had nothing to do with the car's theft will, after explanation, be minimal. (Id. at 442.)