Matt Darisse, a sergeant in the Surry County Sheriff's Department, was sitting in his patrol car on the morning of April 29, 2009. Darisse was monitoring northbound traffic on a stretch of Interstate 77 near Dobson, North Carolina. He says that just around 8:00 a.m. he saw a Ford Escort pass his car. According to Darisse, the driver looked nervous, staring forward and gripping the steering wheel, so he decided to pull onto the road and follow the car. After a few miles, Darisse says the Escort approached some traffic and braked. That's when he noticed that one of the car's brake lights, the right one, was out. It was all the reason he needed, he thought, to initiate a stop.

Darisse approached the car and found two men: Maynor Vasquez behind the wheel and Nicholas Heien lying down under a blanket in the backseat. Darisse asked for Vasquez's license and registration for the vehicle. Both checked out. The sergeant couldn't shake his suspicion of the two, however. Vasquez seemed nervous, Heien remained sprawled out in the backseat throughout the stop, and question as to where the pair was going produced inconsistent answers.

Darisse wanted to search the car. He asked permission from Vasquez, who explained that the vehicle belonged to his friend in the backseat. Heien consented to the search. By this time, another officer had arrived on the scene. The two began a search of the car and Darisse eventually came across a duffle bag. In the side compartment of that duffle, he found a sandwich bag containing 54.2 grams of cocaine. Both men were arrested. Heien was charged with two counts of attempted trafficking. It would have been just another drug bust except for one thing: North Carolina has no law against operating a vehicle with just one brake light.

The Fourth Amendment of the Constitution requires "reasonable suspicion" to justify any police stop. That means that a police officer has to have more than a hunch, but facts or circumstances that might lead a reasonable person to believe that a crime has been or will be committed. Darisse had his hunch about the Ford Escort, but it was the busted brake light that he believed justified stopping the vehicle and initiating the search that would lead to the discovery of cocaine. What he didn't know, however, was the specific language of North Carolina's statute on brake lights.

"No person shall sell or operate on the highway of the State any motor vehicle, motorcycle or motor-driven cycle, manufactured after December 31, 1955, unless it shall be equipped with a stop lamp on the rear of the vehicle…the stop lamp may be incorporated into a unit with one or more other rear lamps."

During his trial, Heien filed a motion to have the evidence in his case suppressed. He argued that he did indeed have a functioning "stop lamp" as required by law. The trial court denied his motion, but The North Carolina Court of Appeals agreed and reversed that decision. After some additional legal back and forth, the case ended up before the Supreme Court of the United States where the nine justices were asked to decide if the Fourth Amendment's requirement for reasonable suspicion is indeed met if an officer's suspicion is based on a mistake of law.

In a ruling of eight to one, the justices decided at the end of last year that ignorance of the law may not be a defense for civilians who break it but it is one for the officers charged with enforcing it. They ruled against Heien, deciding that police officers can make stops based on a misunderstanding of the law without violating the Fourth Amendment. Chief Justice Roberts wrote that the court's decision "does not discourage officers from learning the law." He argued that only objectively reasonable mistakes were permitted in the decision. Such a ruling raises questions, however, about what police officers are indeed required to know of the law and what they can get away with not knowing.

Sonia Sotomayor was the only justice to dissent in the case of Heien v. North Carolina. She is, coincidentally, also the only sitting justice with criminal trial experience. In her dissent, Sotomayor wrote of the "human consequences" when officers make mistakes of law.

"One wonders how a citizen seeking to be law-abiding and to structure his or her behavior to avoid these invasive, frightening, and humiliating encounters could do so," she wrote. "This result is bad for citizens, who need to know their rights and responsibilities, and it is bad for police, who would benefit from clearer direction."

An analysis of nationwide police officer instruction and training standards reveals that police officers learn surprisingly little about the law before they're empowered to enforce it. Hours required for police academy training are relatively short, state officer examinations don't account for legal knowledge and what police officers do know about civilian rights and state law is often undermined by departmental practices.

Requirements to become a police officer vary by state. On average, applicants must be about 21 years of age, possess a valid drivers license, and around two years of college education (which can be substituted in some states with active duty military service.) Officers are also required to complete a few hundred hours of police academy training, instructional and physical, and pass physical and written exams.

The national average of academy training required is just over 600 hours. The bar is much lower in many states, however, particularly in most of the South. Louisiana, for example, requires just 360 hours of training for officer certification. That's compared to the 1,500 hours it requires for barber certification. On the other hand, Washington D.C. requires 1,120 hours of police academy training—more than any other state.

Raymond E. Foster retired as a lieutenant with the Los Angeles Police Department after 24 years of service. Today, he is a police instructor, college lecturer and author, having written 10 books on policing. Foster says, when it comes to legal education, what officers learn in police academies is limited.

"There's probably an hour-long class that focuses on the Bill of Rights, in particular the First, Second, Fourth, Fifth and Eighth Amendments," he says. "Once those are basically covered, then there's another 10 hours that focus on state statutes and court decision that have shaped the way police officers interpret the law."

Not only is the legal education minimal at police academies across the country but the style of instruction also limits officer understanding, according to Foster.

"Much of police academy education is rote memorization," he says. "The academies more or less teach officers to list things and do basic tasks."

More than half of 18,000 police departments and agencies throughout the country use the National Police Officer Selection Test to screen its officers. A 2009 study guide from the U.S. Capitol Police available online describes the exam format as four separately timed test sections. The first three sections use multiple-choice and true-false items to test math skills, reading comprehension and grammar. The last section on incident report writing essentially tests a prospective officer's ability to correctly complete an incident report. Shockingly, the exam contains no items to test for knowledge of the law.

Jenn Rolnick Borchetta was a senior attorney representing thousands of New Yorkers on Floyd v. the City of New York, the class action case that successfully challenged the NYPD's use of Stop and Frisk. She says her experience on Floyd highlighted for her just how little some officers know about the law.

"Officers can recite the legal standard for stops straight out of the law books: to conduct a stop, an officer must have reasonable, articulable suspicion that the person has committed a crime, is committing a crime or is about to commit a crime. I've questioned officers who cannot explain reasonable suspicion beyond that line," says Borchetta. "Officers with years of experience cannot give me one example of what reasonable suspicion looks like."

It is this lack of applied understanding that often results in mistakes of law. It's not just individual officer knowledge, however, but also flawed departmental practices that result in civil rights violations.

"Policing institutions cannot blame widespread constitutional violations—like we saw in the NYPD's stop and frisk practice—on individual officers," Borchetta says. "NYPD brass demanded to see stops, summonses and arrests of young black men, penalized officers who failed to meet stop quotas and refused to discipline officers found by the Civilian Complaint Review Board to have abused their authority in stops of black people. Widespread constitutional violations in policing come from the top down."

Christopher Dunn, associate legal director with the New York Civil Liberties Union agrees.

"Focusing on officer supervision is an important part of having an effectively trained police force," says Dunn. "The most important factor in an officer's conduct on a day-to-day basis is what their supervisor tells them to do."

Last week, the White House and its Task Force on 21st Century Policing released its first report with recommendations for police reform, including improving education and training. The report asks Congress to approve additional funds for education, it endorses scenario-based training and additional training for leadership in police departments and, perhaps most importantly, the report recommends that police academies require basic recruit and in-service officer training on policing in a democratic society.

"Police officers are granted a great deal of authority," it reads, "and it is therefore important that they receive training on the Constitutional basis of and the proper use of that power and authority."

Donovan X. Ramsey is writer based in New York. He's currently a Demos Emerging Voices fellow.

[Illustration by Jim Cooke]

Take our quiz, Are You Smarter Than a Cop? [Note: Four of the quiz questions were pulled from a 2009 US Capitol police department study guide. Actual exams are supervised, timed within each section, and contain more than 70 items in all.]