Instead of seeking a particular suspect based on evidence, predictive profiling attempts to guess which people are likely to commit a crime that hasn't yet occurred.

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Predictive Profiling

With predictive profiling, criminal profiling gets more controversial. Instead of seeking a particular suspect based on evidence at a specific crime, predictive profiling attempts to guess which people are likely to commit a crime that hasn't happened yet.

This isn't a revolutionary idea by itself. Police officers don't just react to crimes: They patrol, observe and try to spot suspicious behavior that could mean a crime is going to take place. Few people would question an officers' right to investigate a suspicious situation or question a suspicious person. Even when police departments use their criminal profiles as a justification for searches and arrests without warrants, those practices have been upheld by the Supreme Court.

Here's an example. State troopers are patrolling a stretch of highway known to be frequented by drug traffickers. The officers know from previous experience that drug traffickers often use rented cars (usually large sedans or SUVs), travel in the very early morning, and put the spare tire in the backseat to leave more room in the trunk for drugs.

At 4:00 a.m., an officer notices a car that fits this profile. The driver is not breaking any major traffic rules, but the trooper pulls the car over anyway, hoping to spot some evidence that could lead to a search of the car. This is considered profiling. The practice of noting criminal tendencies and creating a written profile is sometimes attributed to Florida Highway Patrolman Bob Vogel, although it was probably carried out by others at the same time or prior to Vogel's use of "cumulative similarities."

This kind of profiling can occur when the high-level officials create a policy and program that instructs officers to investigate people who fit a predetermined profile. It can also be part of an unofficial policy, an aspect of the police department's culture passed down from veteran cops to newcomers on the force. Sometimes it simply results from an officer's experience. After years on the job, he has learned what signs might indicate criminal activity.

To determine if such a profile justifies a warrantless arrest or search, the officer must be able to describe the specific factors that led him to believe the suspect was a criminal. A hunch or a feeling won't stand up in court. The following statement probably would:

The suspect appeared nervous and made several contradictory statements. In the back seat, I could see a shoebox full of 35mm film canisters, which drug couriers frequently use to store drugs. The car smelled like air freshener spray, which is often used to cover up the smell of illegal drugs. I spotted the suspect driving slowly up and down a block I know to be frequented by drug dealers.

That kind of profile is not only legal, it's considered good police work.

Some profiling practices come under legal fire because they might violate the U.S. Constitution. Two amendments specifically relate to profiling activity. The Fourth Amendment reads, in whole:

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

Probable cause means that police can't search a home, car or person without some kind of justification -- usually, a reasonable belief that they will find evidence of a crime there, or stop a crime in progress.

Under most circumstances, a police officer can't determine this on his own. He needs a search warrant from a judge, or consent from the person being searched. The main question surrounding profiling is this: If a person fits a criminal profile, in the absence of any other evidence of a crime, does that by itself constitute probable cause? In the case of United States v. Sokolow, the U.S. Supreme Court did decide that a "totality" of evidence leading officers to conclude that the suspect is probably engaged criminal activity is enough to justify an arrest and a search.

The Fourteenth Amendment reads, in part:

No state shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any state deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.

If police officers use criminal profiles that include race as factor, they violate both the Fourth and the Fourteenth Amendment.