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New York City police officers receive a lot of training and instruction, which they're expected to put to good use with honor and integrity on the streets.

Whether that translates to on patrol is one of the main issues surrounding a federal civil rights challenge to some of the nearly 5 million street stops made by police in the past decade. Lawyers for black and Hispanic men who say they have been wrongly stopped by police because of their race have sued the city to force major changes to the contentious police tactic known as stop, question and frisk.

They are trying to show that some wrongful stops happen because officers aren't properly trained or supervised, and they have spent weeks calling witnesses that depict officers as rude, clueless and, often times, racist.

But the city's first witness called Thursday, Deputy Chief James Shea, spoke at length about the training officers receive, both at the police academy and continuing education within the department. He was the former head of the police academy until he was promoted last fall to the chief of department's office in charge of the anti-gang initiative.

Policing in a free society is, like all our other laws, dependent on the consent of the people you're policing.

— NYPD Deputy Chief James Shea

A large part of that training involves how to deal properly with the public, he said, offering a rare window into police behavior.

"Policing in a free society is, like all our other laws, dependent on the consent of the people you're policing," Shea said, and it's important that the public perceive the laws are being enforced fairly and impartially.

"Sometimes even if you are enforcing it in what you believe to be a fair and impartial manner, the method in which you do that leaves the perception that you weren't, and that's damaging," he said. "So we try to make them aware of that all the time so that they're aware, constantly thinking not only of what they're doing but of what perception they're leaving in the mind of the person they're dealing with."

Officers are taught that they must have reasonable suspicion in order to stop someone on the street, a standard lower than probable cause needed to justify an arrest. Like other police officials who testified before him, Shea explained that well-trained officers will use their observational skills as well as intelligence on crime patterns and problems in their precincts to determine whether there is reasonable suspicion to stop someone.

They are taught not to profile. And they are drilled on scenarios both at the academy and in the field to ensure they understand the teachings, Shea said.

Attorney Brenda Cooke showed a police training video that explained how officers should learn to look for weapons: a sagging coat, a person constantly checking his or her side or touching his or her waist, someone who runs from police or makes an abrupt turn, and a person with a suspicious bulge in his or her pants.

But none of those indicators alone mean someone actually has a weapon — and officers can't assume. They have to use discretion whether to frisk someone, and they can't just rifle through pockets. About half of those stopped are frisked.

"When I was a police officer, if someone had a bulge at their waistband it was probably, unless they were carrying tools, it was probably a firearm," said Shea, who joined the department in 1991. "Now a majority of the population carries cellphones. So they had to be trained that you have to feel it. You know what people ordinarily carry."

Many of the plaintiffs in the class-action lawsuit have testified they felt the stop was unfair, the officer didn't have reasonable suspicion and they weren't treated with respect. In some cases, the stopping officer's testimony contradicted those claims.

For example, Clive Lino, 32, testified that he was stopped and interrogated by police for 20 minutes because of his red leather jacket, branded Pelle Pelle. He said he believed he was stopped because he was black. Later, the two officers who stopped him testified that their precinct commander handed out a poster of an unsolved killing that mentioned the suspect was male, black, about 6 feet tall and wearing a loose-fitting red leather Pelle jacket.

It's up to the police to explain to someone who was stopped why it happened, Shea said.

"Sometimes people are mad. It's not pleasant to be stopped by the police," Shea said. "Even if they don't understand it at that moment, if you do the right thing, then maybe later even, it will sink in — and when they're not in the immediate moment of being stopped and they have a chance to think about it."

His testimony continues Monday. The trial has been underway for more than a month. U.S. District Court Judge Shira Scheindlin has the power to order major changes to the police department and has already expressed concerns about the tactic.