For example, if an officer on patrol hears a radio dispatch that describes a red sedan fleeing the scene of a robbery, the officer does not have probable cause to pull over every red sedan in sight. If the dispatcher tells the officer that the sedan is missing a hub cab, has an orange bumper sticker and is occupied by four people, and the officer spots a car matching those terms, that would be probable cause to effect a stop.
Lacking probable cause does not necessarily leave an officer powerless. Reasonable suspicion is a notch below probable cause, but it does come with its privileges. Reason suspicion is not as stable as probable cause, nor does reasonable suspicion require a strong supportive basis. A simple reasonable belief, based on a general observation or circumstance, and possibly supported by experience, may be enough to investigate further or take minimal action. Having mere suspicion is not of much value. Mere suspicion is a hunch of instinctive feeling that something may be wrong. Mere suspicion may increase an officer's awareness toward a person or property but it cannot be any principle for action (Bohm and Haley, 2002).
Sources of probable cause include many possibilities. A superior officer may provide a fellow officer with the knowledge pertaining to a crime that could be used later as a factor in a search or arrest. An anonymous telephone call with specific information, a tip from a reliable citizen in the community or a specialized officer in the field with expertise may provide information to supplement probable cause. Sometimes personal observations alone or any combination of these can be enough to establish probable cause (Garland & Stuckey, 2000). An informant's role in probable cause has been questioned and clarified by the courts on more than one occasion. Illinois vs. Gates pointed out that an informant's knowledge should be taken into account but not rigidly applied.