New York: In more than six years of spying on Muslim neighbourhoods, eavesdropping on conversations and cataloguing mosques, the New York Police Department’s secret Demographics Unit never generated a lead or triggered a terrorism investigation, the department acknowledged in court testimony unsealed late Monday.

The Demographics Unit is at the heart of a police spying programme, built with help from the CIA, which assembled databases on where Muslims lived, shopped, worked and prayed. Police infiltrated Muslim student groups, put informants in mosques, monitored sermons and catalogued every Muslim in New York who adopted new, Americanised surnames.

Police hoped the Demographics Unit would serve as an early warning system for terrorism. And if police ever got a tip about, say, an Afghan terrorist in the city, they’d know where he was likely to rent a room, buy groceries and watch sports.

But in a June 28 deposition as part of a longstanding federal civil rights case, Assistant Chief Thomas Galati said none of the conversations the officers overheard ever led to a case.

“Related to Demographics,” Galati testified that information that has come in “has not commenced an investigation.”

The NYPD is the largest police department in the nation and Mayor Michael Bloomberg has held up its counter-terrorism tactics as a model for the rest of the country. After AP began reporting on those tactics last year, supporters argued that the Demographics Unit was central to keeping the city safe. Galati testified that it was an important tool, but conceded it had not generated any leads.

“I never made a lead from rhetoric that came from a Demographics report, and I’m here since 2006,” he said. “I don’t recall other ones prior to my arrival. Again, that’s always a possibility. I am not aware of any.”

Galati, the commanding officer of the NYPD Intelligence Division, offered the first official look at the Demographics Unit, which the NYPD denied ever existed when it was revealed by the AP last year. He described how police gather information on people even when there is no evidence of wrongdoing, simply because of their ethnicity and native language.

As a rule, Galati said, a business can be labelled a “location of concern” whenever police can expect to find groups of Middle Easterners there.

Galati testified as part of a lawsuit that began in 1971 over NYPD spying on students, civil rights groups and suspected Communist sympathisers during the 1950s and 1960s. The lawsuit, known as the Handschu case, resulted in federal guidelines that prohibit the NYPD from collecting information about political speech unless it is related to potential terrorism.

Civil rights lawyers believe the Demographics Unit violated those rules. Documents obtained by the AP show the unit conducted operations outside its jurisdiction, including in New Jersey. The FBI there said those operations damaged its partnerships with Muslims and jeopardised national security.

In one instance discussed in the testimony, plainclothes NYPD officers known as “rakers” overheard two Pakistani men complaining about airport security policies that they believed unfairly singled out Muslims. They bemoaned what they saw as the nation’s anti-Muslim sentiment since the 2001 terrorist attacks.

Galati said police were allowed to collect that information because the men spoke Urdu, a fact that could help police find potential terrorists in the future.

“I’m seeing Urdu. I’m seeing them identify the individuals involved in that are Pakistani,” Galati explained. “I’m using that information for me to determine that this would be a kind of place that a terrorist would be comfortable in.”

He added, “Most Urdu speakers from that region would be of concern, so that’s why it’s important to me.”

About 15 million Pakistanis and 60 million Indians speak Urdu. Along with English, it is one of the national languages of Pakistan.

In another example, Galati said, eavesdropping on a conversation in a Lebanese cafe could be useful, even if the topic is innocuous. Analysts might be able to determine that the customers were from South Lebanon, he said, adding, “That may be an indicator of possibility that is a sympathiser to Hezbollah because Southern Lebanon is dominated by Hezbollah.”

After the AP began reporting on the Demographics Unit, the department’s former senior analyst, Mitchell Siber, said the unit provided the tip that ultimately led to a case against a bookstore clerk who was convicted of plotting to bomb the Herald Square subway station in Manhattan. Galati testified that he could find no evidence of that.

Attorney Jethro Eisenstein, who filed the Handschu case more than 40 years ago and questioned Galati during the deposition, said he will go back to court soon to ask that the Demographics Unit be shut down. It operates today under a new name, the Zone Assessment Unit. It recently stopped operating out of state, Galati said.

“This is a terribly pernicious set of policies,” Eisenstein said. “No other group since the Japanese Americans in Second World War has been subjected to this kind of widespread public policy.”

Dozens of members of Congress have asked the Justice Department to investigate the NYPD. Attorney General Eric Holder has said he was disturbed by the reports. But John Brennan, President Barack Obama’s top counterterrorism adviser, has said he is confident the NYPD’s activities are lawful and have kept the city safe.