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What Everyone Should Understand About Police Encounters

Updated on September 5, 2011

The concepts of reasonable suspicion and probable cause

Reasonable suspicion occurs when unusual conduct is combined with certain articulable facts that may indicate a person having committed or is intending to commit a crime. The greater the number of facts and observations there are, the greater the reliability of reasonable suspicion. Reasonable suspicion can be invoked if for example, a person flees the police while in a high crime area as in Illinois v. Wardlow (2000), a person matches a “wanted” poster, as in the case of United States v. Hensley (1985), the receiving of anonymous tips combined with officer observations as in Alabama v. White (1990), or the totality of circumstances as in United States v. Arvizu (2001). Reasonable suspicion does not encompass any proof of criminal activity, however, it does allow law enforcement officers to stop and question the suspected individual. Probable cause is a higher evidentiary standard than reasonable suspicion. Probable cause is the concept that an offense has been committed and the suspect has a direct link to the crime. Mathematically, probable cause exists when there is over a 50 percent certainty that an individual has committed an offense or that items being sought are in a particular place. Probable cause must exist to make arrests, with or without a warrant, and to engage in a search, with or without a warrant. For probable cause to be valid in an arrest or search, it is most often because of a totality of circumstances. For example, probable cause was ruled valid in the case Illinois v. Gates (1993) because of the receiving of an anonymous letter which provided information and the resulting surveillance of police officers. In United States v. Sokolow (1989) the combination of an individual matching a drug currier profile and the indication of concealed narcotics detected by a drug-sniffing dog provided enough probable cause to allow a search.

Examples of reasonable suspicion and probable cause

An example of reasonable suspicion can be provided by the circumstances of Alabama v. White (1990). The facts of this case were that law enforcement officials received an anonymous phone call regarding the possession of an ounce of cocaine. The anonymous tip provided the color and make of the car of the suspect, the time the suspect would be leaving, the destination and the fact that a taillight was broken. Following this lead, the police set up surveillance and all of the identifying circumstances provided by the caller were evident. Having established reasonable suspicion, a stop was made. The Supreme Court ruled that there was sufficient reasonable suspicion and the stop was valid. The results of the stop led to permission to search an attaché where marijuana was found, leading to an arrest. The arrest allowed a further search where the cocaine was discovered in a purse. At issue was whether or not an anonymous tip coupled with the police work constituted reasonable suspicion, and it was ruled that it did. A case that is similar to Alabama v. White, but where probable cause was deemed valid, was Draper v. United States (1959). In this case, a paid informant supplied information to a narcotics agent regarding the transport of heroin from Chicago to Denver via train. The informant gave the agent a detailed physical description of the man, the two possible dates he would be arriving, and the fact he was a very fast walker. A surveillance of all trains from Chicago to Denver resulted and when a man who exactly matched the description arrived, he was arrested. After the arrest, a search reveled heroin and a syringe. At issue in this case was whether or not information from an informer coupled with officer corroboration validated probable cause. It was ruled that it did because of the past reliability of the informant, the fact that he was employed for the purpose and the verification of the information by officers. The significant difference between Alabama v. White and Draper v. United States is that in the former, information was received from an anonymous tip and in the latter from a paid reliable informer. The first case resulted in reasonable suspicion and the second case resulted in probable cause.

The differences in stopping and detaining a suspect

In order for a law enforcement officer to stop a person, the officer need only have a reasonable suspicion that crime is afoot. In Terry v. Ohio (1968) it was ruled that a stop is justified if it is prompted by unusual conduct leading to the suspicion that a criminal act is impending or already committed. This ruling allows officers to stop a person without probable cause being established. Probable cause is not needed if a full-scale search will not be conducted. During a stop, an officer may question the person and pat-down the person for weapons on the outside of his or her clothing. However, during a stop, the person cannot be detained or feel as if he or she is in custody. Therefore, detaining a suspect occurs when that person is no longer free to leave. However, the detention must be of a short duration and limited in its scope. In United States v. Sharpe (1985) it was determined that a suspect can be “detained for a period of 20 minutes while officers conduct a limited investigation of suspected criminal activity”. In other words, what determines the difference between whether a suspect has been stopped or detained, is the amount of freedom of movement that remains for the suspect. For a stop, a person’s freedom of movement remains complete, whereas during a detention, freedom of movement is temporarily limited. As a point of comparison, for an arrest, a person’s freedom of movement is taken away altogether.

Where an officer can search after making a legal arrest of a suspect

Generally, following a legal arrest, an officer is allowed to make a full search of the individual and the immediate vicinity. Arrests can be made with or without a warrant, as can searches. In Chimel v. California (1969) the Supreme Court ruled that after making a legal arrest, this time with a warrant, a search of the immediate area can be conducted even though a search warrant was not issued. The search was deemed valid since it was considered to be done to ensure officer safety and to prevent the destruction of evidence. Though limited to a search of the immediate area, the parameters of the area are not completely defined. Some courts have said the immediate area is only a person’s wingspan and other courts have broadened the area to whole rooms. In Vale v. Louisiana (1970) the Supreme Court ruled that the house of an arrested person cannot be searched without a warrant unless the arrest actually took place in the house. In this case, the arrest for narcotics took place on the front steps of the house. It was further ruled that officers erred in their house search because of a lack of exigent circumstances and specifically established and well-delineated exceptions. Body searches were ruled valid after a full custody arrest in United States v. Robinson (1973) ,but even though not addressed by the Supreme Court, lower courts deny body cavity searches in a typical arrest because of their unconstitutionality.


The concept of probable cause is an important one to understand. If probable cause, or a high level of certainty that a crime is about to be committed or has been committed, exists then an arrest and a search can be made. Probable cause requires facts and observations that would lead any reasonable person to believe criminal activity is afoot, not just a suspicion of such. This rule is important because of its determination in restricting people’s Fourth Amendment rights. If it is determined probable cause exists, a person’s freedoms can be restricted or denied. For this reason, solid and valid evidence, facts, observations and information have to be present to prevent unnecessary and unsubstantiated limits to individuals’ freedoms. Requiring valid probable cause to conduct arrests and searches protects citizens’ constitutional rights. It controls police authority in the cases of warrantless arrests and searches and guides the determinations of judges and magistrates in issuing arrest and search warrants. The relevance of the Fourth Amendment to the area of criminal justice is profound because it ensures the right of people to be secure in their persons, houses, papers and effects against unreasonable searches and seizures and shall not be violated except upon probable cause.


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