The New York City Police Department is invoking a concept frequently employed by intelligence agencies like the FBI and CIA to deny a request for financial records on the unit that surveils Muslim communities.

Even to release a budget for the secretive Zone Assessment Unit, the NYPD claimed in a letter to HuffPost, would allow someone to "form a mosaic that depicts covert public safety activities that would be jeopardized."

The NYPD's denial of appeal was issued Dec. 6, which comes 10 months after the initial request was made under the state Freedom of Information Law, in the waning days of Commissioner Raymond Kelly's tenure. National security lawyers and a New York state public records expert told HuffPost they have never seen a local law enforcement agency invoke the so-called mosaic theory, which was frequently cited by the administration of President George W. Bush to deny federal information requests.

"There may be more behind the theory here than what appears in this three-page document, but it looks on its face to be an unsubstantiated invocation of the mosaic theory," said Columbia University law professor David Pozen, a widely cited expert on the concept. "This on its face is a pretty bare assertion of potential harm that's hard to argue against -- because it's hard to know what their theory is."

First brought to prominence during Ronald Reagan's presidency, the mosaic theory holds that enemies of the state can assemble disparate, even seemingly innocuous pieces of information to uncover national security secrets. Under Reagan, the FBI even sought to track library users' borrowing habits, a practice that was revived under the Patriot Act.

Courts have cited mosaic theory to withhold information sought from the FBI, the CIA and the NSA under the federal Freedom of Information Act, concluding that documents that might otherwise be released to the public can be withheld by agencies because such information could help foreign adversaries assemble that "mosaic." In the wake of the Sept. 11 attacks, the Bush administration frequently stood on the mosaic theory to persuade courts to reject FOIA lawsuits. Pozen and others have criticized judges for not testing the government's assertions of mosaic theory strongly enough.

For the NYPD to cite mosaic theory struck experts whom HuffPost contacted as unusual, given that local law enforcement is generally charged with solving crimes, not pursuing national security investigations. But under the command of Kelly and the Intelligence Division's Deputy Commissioner David Cohen, a CIA veteran, the department has increasingly behaved like a federal intelligence agency.

The NYPD did not respond to a request for comment on its use of mosaic theory. But in a legal declaration in October, Cohen said that "it should be kept in mind that as part of NYPD's efforts to prevent or anticipate unlawful activity, including terrorist acts, the Intelligence Bureau may initiate investigations in advance of unlawful activity occurring and that such investigations may be discontinued without an arrest or prosecution for a variety of reasons."

"Simply put," he added, "disclosure of virtually any documents that concern open or discontinued investigations may interfere with a pending or contemplated investigation."

A state judge in May denied a coalition's request for investigative documents from the NYPD's Intelligence Division, citing in part Cohen's fear that such documents could contain "strands" of information that might be used to reconstruct police sources and methods.

The Huffington Post did not request records related to individual investigations, but general budget and financial documents. For the department to claim, as it did in Records Access Appeals Officer Jonathan David's letter to HuffPost, that even budget documents are exempt from disclosure because they "could endanger the [sic] both civilians and undercover officers who [sic] involved in investigations" struck one government secrecy expert as far-fetched.

"My hope would be that if this theory is raised in New York, that a state judge would say, 'Show me, police department, show me how the public safety could be hurt' -- and I don't believe that can be met," said Bob Freeman, executive director of the New York State Committee on Open Government.

Freeman, one of the state's leading authorities on FOIL law, said he has never seen a local law enforcement agency deny a records request on the basis of the mosaic theory. Nor has Jeffrey Light, a lawyer who litigates both federal FOIA lawsuits relating to intelligence agencies and Washington, D.C., police public records requests.

The NYPD also denied HuffPost's requests for information on policies relating to its cooperation with foreign governments under the International Liaison Program, which has placed NYPD officers in a dozen foreign countries to report on terror attacks. The NYPD stated that it had no records of such policies. The department also rejected requests for records on financial support from the New York City Police Foundation and federal agencies like the White House's High Intensity Drug Trafficking Area program. The Associated Press revealed last year that White House funds had been used to pay for Zone Assessment Unit vehicles and computers.

In addition to the mosaic theory, the NYPD also cited a slew of reasons why it couldn't release the records, ranging from the fear that they might reveal confidential sources and information, to ongoing litigation against NYPD spying, to a public records law exemption for intra-agency privilege. It did not cite which exemptions were being applied to which records requests.

The Huffington Post is reviewing its legal options as Mayor Michael Bloomberg and Kelly are succeeded by incoming New York City Mayor Bill de Blasio and NYPD Commissioner Bill Bratton.

As the city's public advocate, de Blasio released a report that faulted the NYPD for frequently ignoring and rejecting legitimate public records requests. In interviews during his final days, Kelly criticized media organizations for their coverage of issues like stop-and-frisk stops, and the department has ordered local precincts not to release police blotter information to neighborhood news organizations.

New York City Councilman Brad Lander (D) told HuffPost in March that the NYPD had also failed to provide him with detailed budget information on the Intelligence Division.

Freeman said he believes the budget documents should be released under Freedom of Information Law, with appropriate but specific redactions to protect public safety.