This week a federal judge adjourned proceedings in one of the most significant challenges yet to stop-and-frisk in New York City, and scheduled what are sure to be impassioned closing statements for early November.

The eight days of testimony at Manhattan’s federal courthouse in the Ligon v. City of New York lawsuit struck at one of the fundamental questions of the New York City Police Department’s stop-and-frisk practices: whether police are acting lawfully when they stop hundreds of thousands of people (but largely black and Latino males) each year, or whether their crime prevention tactics are in fact a widespread pattern of police violating citizens’ freedoms.

While the debate is emotional and political on the streets and editorial pages of the city, in the courtroom it’s largely a matter of deciphering the letter of the law, or what is known as the “De Bour Standard.” Since 1976, judges have used the state Court of Appeals opinion in People v. De Bour to clarify the rights of citizens and powers of police when it comes to search and seizures.

“This whole stop-and-frisk debate has gone on without recognition that there is a legal subtext that is crucial,” said Eugene O’Donnell, a lecturer on law and at John Jay College of Criminal Justice. “It’s sort of been ignored, the reality that when police interact with people there is a very complicated set of rules that the courts have set forth.”

Legal guide adapted from Brian H. Lowy, Queens College. To save on a smartphone, click the image and add to homescreen.

In De Bour, the state’s highest court sought to determine whether a police officer can approach a citizen on the street and request information, even in the “absence of any concrete indication of criminality.”

In its decision, written by former Chief Judge Sol Wachtler, the court found that intrusions on “the security and privacy of the individual…with intent to harass…based upon mere whim, caprice or idle curiosity” would violate a person’s rights, but that with “some articulable reason sufficient to justify the police action” officers have the right to engage citizens.

To clarify what those reasons might be and protect citizens from unlawful intrusions by police, the court issued a four-tiered guideline to judge the constitutionality of police conduct proportionate to the behavior of an individual under an officer’s gaze.

Though the De Bour Standard attempts to be strict in its guidelines, it is challenging enough to apply to individual cases that some legal experts say it is practically “esoteric” and “indecipherable.” And in the context of Ligon, where questions about trespass affidavit programs, high-crime neighborhoods, and public space vs. private property are also in play, the legal terrain is particularly murky.

In Ligon, 12 plaintiffs represented by the New York Civil Liberties Union claim that New York Police Department officers violated their Fourth Amendment constitutional rights by stopping or arresting them for trespassing simply because they were inside or near buildings enrolled in the city’s trespass affidavit program.

The program, also known as “Operation Clean Halls” or “TAP,” has been used in thousands of privately owned buildings since 1991, when police launched it as a way to target rampant drug dealing. Landlords in Clean Halls sign affidavits giving their consent for police to patrol their buildings and arrest people for criminal activity, including trespassing.

The NYCLU claims the program has led to an assault of the liberty of New Yorkers to leave or return to their residences freely, or visit friends and family in their homes. The plaintiffs’ complaint contains a multitude of stories of individuals being arrested for trespassing for standing outside of buildings while waiting for family members or exiting a building.

Over the course of the week, the city’s Corporation Counsel seeded doubts about the analysis of stop-and-frisk data by the NYCLU’s expert witnesses, including Columbia Law School professor Jeffrey Fagan, and called on witnesses from within the police department as well as a manager of a TAP building to testify to the effectiveness of Operation Clean Halls in combating crime.

Presiding Judge Shira Scheindlin, who currently has three cases before her challenging the city’s stop-and-frisk policies, is sure to consider a multitude of questions when she issues a decision in Ligon. Can a person standing on the sidewalk in front of a TAP building be stopped by a police officer or charged with trespassing? Does a neighborhood or building with high levels of crime give police reasonable suspicion to stop anyone on the premises of a trespass affidavit building? What are the rights of residents inside buildings enrolled in Operation Clean Halls?

But Scheindlin is almost definitely not going to challenge the precedent of De Bour itself, suggests O’Donnell. The plaintiffs have not called for such changes, but more than that it is hard to imagine that, farcically complicated as they are, they could be improved.

“You have state and federal constitutional protections, and it’s hard to have a really simple standard,” said O’Donnell. “There is a limitless number of scenarios that police find themselves in. That is a very big gray area.”

Last week, the executive director of the NYPD’s Legal Bureau, Inspector Kerry Sweet, testified in the Ligon case that the department began to review its policies for patrolling housing projects and TAP buildings in 2010, after a “great deal of internal debate over the role of officers in NYCHA buildings.” Were they in effect doormen who could question anyone coming in and out buildings?

The NYPD department subsequently issued two interim orders, recalled Sweet, that sought to clarify proper procedure for police officers in Clean Halls buildings and the requirements of De Bour. One of them, “Interim Order 23,” states that an “officer may not stop (temporarily detain) a suspected trespasser unless the officer reasonably suspects that the person is in the building without authority.”

The orders force “officers to think about probable cause,” said Inspector Sweet on the witness stand. But in instances where an individual refuses to explain his or her presence in a TAP building or cannot do so — but is not involved in any identifiable criminal activity — police officers are in a “kind of gray area,” he said. “If people are uncooperative but we don’t have probable cause, we can ask them to leave.”

“If someone is merely exiting a building, we don’t have to engage them,” said Sweet.

Judge Scheindlin asked Sweet whether such a stop would be justified if the only other factor was that the building was in a high-crime neighborhood.

“That to me would not be enough,” said Sweet. His response appeared to bolster the testimony of several of the plaintiffs, who during the trial described wrongful stops and arrests from police entering or leaving TAP buildings.

As confusing as it is for police officers and the courts to apply the De Bour Standard, it can be nearly impossible for citizens, who are usually unaware of its existence or the specifics of their constitutional rights when it comes to interacting with police.

During his testimony last week in the Ligon case, 24-year-old plaintiff Abdullah Turner, who has been stopped by police officers in the Bronx several times and was arrested for trespassing outside a Clean Halls building in 2011, explained why he did not feel free to leave when stopped by police, even if he believed he was doing nothing illegal.

“I don’t know anyone else who has walked away from a cop in the middle of a conversation,” said Turner.

His arrest for trespassing, resulting in a 24-hour stay in jail, and ultimate dismissal of charges made Turner feel defenseless, he said. “When you’re a kid, you turn to your parents for protection. When you’re an adult, you go to the police. But where are you going to go when the police are harassing you?”