What Could Justify a Detention?
The Supreme Court has considered several common circumstances that might be relied on by law enforcement officers to initiate an investigative detention. These cases create a list of factors that can be used to show that a ped stop or car stop was reasonable under the Fourth Amendment.
Collective knowledge: "Effective law enforcement cannot be conducted unless police officers can act on directions and information transmitted by one officer to another. This rule is a matter of common sense and enables officers in one jurisdiction to act promptly in reliance on information from another jurisdiction." (US v. Hensley)
The "collective knowledge doctrine" permits a vehicle stop based on a wanted flier, a radio broadcast, or an NCIC hit. It also permits a sergeant or detective who sees a suspected impaired driver to radio the pertinent information to a patrol officer, who can then lawfully stop the vehicle.
Observations, training, and experience: "When discussing how reviewing courts should make reasonable-suspicion determinations, we have repeatedly said that they must look at the totality of the circumstances of each case to see whether the officer has a particularized and objective basis for suspecting legal wrongdoing. This process allows officers to draw on their own experience and specialized training to make inferences from and deductions about the cumulative information available to them that might well elude an untrained person." (US v. Arvizu)
Drug courier profiles: Although hunches and racial profiles cannot form the basis of a stop, specific traits of particular kinds of criminals may. For example, a nervous traveler who buys a roundtrip airline ticket from a drug source city to a distribution hub with only hours before the turnaround and who pays cash and carries no luggage, fits a courier profile known to well-trained narcotics investigators, justifying an investigative detention. (US v. Sokolow)
Unprovoked flight in a high-crime area: There is nothing particularly suspicious about a person's mere presence in a high-crime area, since some people live in such places or must travel through them. (Brown v. Texas) However, when a marked police car pulls into a high-crime area and people start running away for no apparent reason, this is reasonable suspicion to stop them. "Headlong flight-wherever it occurs-is the consummate act of evasion: it is not necessarily indicative of wrongdoing, but is certainly suggestive of such." (Illinois v. Wardlow)
Traffic violations: An officer who suspects the driver or passengers of a vehicle of criminal behavior is allowed to use an observed traffic violation as a reason to stop the vehicle for a brief investigation, during which observations and questioning may establish PC for an arrest. (Arkansas v. Sullivan; Virginia v. Moore)
Checkpoints: Law enforcement agencies may establish detention checkpoints to look for illegal aliens entering the country (US v. Cortez), to check for unlicensed drivers (Delaware v. Prouse; Texas v. Brown), to screen drivers for impairment (Michigan v. Sitz), to solicit witnesses to a recent crime (Illinois v. Lidster), or to catch a dangerous criminal who is likely to use a particular escape route. (Indianapolis v. Edmond)
Length of Detentions
"In assessing whether a detention is too long in duration to be justified as an investigative stop, we consider it appropriate to examine whether the police diligently pursued a means of investigation that was likely to confirm or dispel their suspicions quickly." (US v. Sharpe) There is no set time limit on detentions; the length of the detention will depend on the circumstances. "Police often are not yet aware of the exact sequence and scope of events they are investigating-indeed, that is why police must investigate in the first place." (Texas v. Cobb)
Devallis Rutledge is a former police officer and veteran prosecutor who currently serves as Special Counsel to the Los Angeles County District Attorney. He is the author of 12 books, including "Investigative Constitutional Law."