Campaigners for greater accountability at New York's powerful police force have seized on a report that details for the first time the extent of the collaboration between the CIA and the NYPD in the years after 9/11.

The formerly classified inspector-general's report also raises new questions over whether the spy agency's partnership with the nation's largest police department amounted to unofficial cover for CIA officers to operate in the US in ways that could otherwise be deemed unlawful.

The 12-page document, first described in a New York Times article published on Wednesday night, contains the December 2011 findings of an investigation into the CIA's training and support of the NYPD that included embedding four officers in the department in the decade following the September 11 attacks.

According to the report, one of the individuals engaged in surveillance operations on US soil and believed there were "no limitations" on his activities. The report said another officer was given "unfiltered" access to police reports that had nothing to do with foreign intelligence.

The partnership led to "irregular personnel practices" devoid of "formal documentation in some important instances", CIA inspector David Buckley found. While the review found no agency employees in violation of the law and Buckley determined "an insufficient basis to merit a full investigation" into the partnership, the inspector-general said the "risks associated with the agency's relationship with NYPD were not fully considered and that there was inadequate direction and control by the agency managers responsible for the relationship".

The inquiry was prompted by a Pulitzer Prize-winning series of investigative stories by the Associated Press into the NYPD's intelligence division. David Cohen, a veteran CIA officer with no police experience, was the architect of the NYPD's spy programme and remains the department's deputy commissioner for intelligence. The AP found that under Cohen and commissioner Ray Kelly, the intelligence division targeted more than 250 mosques along the east coast, infiltrated student groups and mapped Muslim neighbourhoods for surveillance.

The NYPD has steadfastly defended its efforts, arguing that its counterterrorism operations have stopped 14 terrorist plots since 2001, although that claim has been contested in the case of almost every alleged plot.

"We're proud of our relationship with CIA and its training," NYPD spokesman Paul Browne told the New York Times. Terrorists "keep coming and we keep pushing back", he said.

In an extended interview with the Wall Street Journal in April, Kelly was asked if changes had been made to the NYPD's surveillance programs in the wake of the AP series. "No," he said.

Speaking to the Guardian on Thursday, NYPD critics expressed concern over the details revealed in the IG report.

"This is deeply troubling because, at the very least, it's clear that there was insufficient legal guidance and oversight for this relationship," Hina Shamsi, director of the ACLU's national security project, said. Shamsi is a lead attorney on a lawsuit filed last week on behalf of several Muslims and Islamic organisations accusing the NYPD of unlawful surveillance.

"A key question is what information went back and forth between people even if they, at least formally, appear to have severed their relationship with the CIA," she said. "It is very clear that there was insufficient legal guidance and oversight and that what should be a clear firewall between the CIA and local law enforcement, in terms of law enforcement and intelligence gathering, appears to be porous."

Shamsi said "the extent to which these people who were from the CIA had access to CIA databases, operations and information while they were embedded with the NYPD" remained murky. "That's the thing the report doesn't address," she said.

Faiza Patel, co-director of the Liberty and National Security Program at the Brennan Center for Justice at the New York University School of Law, said in an email to the Guardian that the report confirmed much of what had been reported or suspected in previous years, but expressed fear that the police department had internalised the worldview of an intelligence agency.

"We already knew that the CIA inspector-general was concerned about irregularities in the assignment of CIA officers to the NYPD. The IG report shows that the concern was more serious than personnel issues, but touched on the agency's involvement in purely domestic intelligence operations," she said.

Patel said that "at least one CIA analyst claimed that he was given unfettered access to NYPD intelligence reports" but said "the bigger issue, in my mind, is the extent to which the CIA's way of working influenced the NYPD's intelligence program".

"Brooklyn is not Baghdad," Patel said. "All New Yorkers have a stake in the city's safety and should be treated as partners in fighting crime and terrorism. The CIA, of course, operates in very different environments. My concern is that a mindset forged in counter-insurgency operations unduly shaped the NYPD's intelligence operations, especially its Muslim surveillance program."

The Freedom of Information Act that eventually resulted in the disclosure of the inspector-general's report was filed on 28 March 2012 by Ginger McCall, director of the open government project at the Electronic Privacy Information Center in Washington DC.



The IG report showed the CIA had been dishonest in describing its relationship with the NYPD, McCall told the Guardian.

"The report indicates that the CIA was not forthright with the American public about its activities," she said, noting that the review detailed the work of four CIA employees with the department. Previous reporting had indicated there were only two. Some of those individuals, McCall said, "did have the opportunity to participate in domestic surveillance and domestic-focused investigations".

Attorney Jethro Eisenstein has been at the head of a four-decade lawsuit accusing the NYPD of violating a set of department rules prohibiting the investigation of political activity in the absence of an indication of illegal activity. Known as Handschu, the rules were developed in response to the department's past surveillance of radical and activist groups. The rules are now at the heart of the legal debate over the NYPD's CIA-backed surveillance of Muslim communities.

Speaking to the Guardian, Eisenstein paraphrased the CIA's assessment of its work with the NYPD, as described in the IG report as: "'We were very sloppy in dealing with the NYPD, and maybe we got too deep in bed with them, and maybe we shouldn't be doing that.'"

Eisenstein said Cohen's appointment to the department brought about a dangerous shift. "Once Cohen came aboard, the whole ethos of the place changed," he said. "They stopped being cops. They started being an intelligence agency. As far as intelligence agencies are concerned, the more information about the more people, the better. And that's contrary to what the Handschu rules say."

"It's a whole different mindset. Law enforcement is about identifying, stopping illegal activity or apprehending people who have engaged in illegal activity. It's a totally different model from intelligence gathering," he said. Eisenstein said the shift represented "a huge danger".

A veteran NYPD reporter and author of the book NYPD Confidential, Leonard Levitt, said Michael Bloomberg's successor as mayor should launch an independent commission to investigate the police department.

"Somebody needs to look at what's gone on in these 12 years," Levitt said.