The first systematic look at the New York police department's response to Occupy Wall Street protests paints a damning picture of an out-of-control and aggressive organization that routinely acted beyond its powers.

In a report that followed an eight-month study (pdf), researchers at the law schools of NYU and Fordham accuse the NYPD of deploying unnecessarily aggressive force, obstructing press freedoms and making arbitrary and baseless arrests.

The study, published on Wednesday, found evidence that police made violent late-night raids on peaceful encampments, obstructed independent legal monitors and was opaque about its policies.

The NYPD report is the first of a series to look at how police authorities in five US cities, including Oakland and Boston, have treated the Occupy movement since it began in September 2011. The research concludes that there now is a systematic effort by authorities to suppress protests, even when these are lawful and pose no threat to the public.

Sarah Knuckey, a professor of law at NYU, said: "All the case studies we collected show the police are violating basic rights consistently, and the level of impunity is shocking".

To be launched over the coming months, the reports are being done under the Protest and Assembly Rights Project, a national consortium of law school clinics addressing America's response to Occupy Wall Street.

The NYPD appears to be the worst offender, in large part because it has made little attempt – unlike Oakland, for example – to reassess its practices or open itself up to dialogue or review. The NYPD practices documented in the report include:

• Aggressive, unnecessary and excessive police force against peaceful protesters, bystanders, legal observers, and journalists. This included the use of batons, pepper spray, metal barricades, scooters, and horses.

• Obstruction of press freedoms and independent legal monitoring, including arrests of at least 10 journalists, and multiple cases of preventing journalists from reporting on protests or barring and evicting them from specific sites.

• Pervasive surveillance of peaceful political activity.

• Violent late-night raids on peaceful encampments.

• Unjustified closure of public spaces, dispersal of peaceful assemblies, and trapping of protesters.

• Arbitrary and selective rule enforcement and baseless arrests.

• Failures to ensure transparency about government policies.

• Failures to ensure accountability for those allegedly responsible for abuses.

The report argues that the lack of transparency and accountability is especially troubling because the public does not know whether police actions are guided by specific written policies, or whether they are random or ad hoc.

The NYPD turned down multiple requests to meet the researchers, who say they were keen include the police's point of view in the report. The other four police departments examined for the project all sent representatives to meet researchers. The NYPD did not provide a comment to the Guardian by the time of publication of this article.

In New York, researchers had to obtain documents by filing freedom of information requests with the NYPD, and Knuckey said some requests have still not been answered. The researchers also requested meetings with the mayor, Michael Bloomberg, the department of parks and recreation, the public advocate, and the district attorney's office, none of whom responded.

Researchers reviewed hours of video footage, documents and press reports, as well as conducting interviews with protestors and witnesses. "Many interviewees cried while speaking about their interaction with the police – they still carried a sense of trauma," Knuckey said,.

As a legal observer during the Occupy protests, Knuckey recalled being subjected to verbal abuse, arrested and witnessed fellow police officers covering for errant colleagues. "The message all of this sends out, especially to younger officers in the force, is one of impunity," she said.

The report lists a total of 130 incidents of excessive or unwarranted force, which, it says, require investigation by authorities. To date, only one NYPD officer – deputy inspector Anthony Bologna, who pepper-sprayed several female protesters on 24 September 2011 – has faced disciplinary proceedings for using excessive force during the Occupy protests.

The report makes a host of recommendations around investigation of abuses, transparency, policy review and reformulation, and setting up external oversight. NYU and Fordham are also making the report the basis of written complaints made today to Bloomberg and the NYPD, the state department of justice as well as the United Nations.

Raising the matter with the the international body is especially important, Knuckey said, because there have been instances of authorities in Egypt, Syria and Indonesia pointing to NYPD actions to justify their own and far more severe crackdowns on non-violent protests.

"The point needs to be made that the NYPD does not exemplify international human rights law, it violates it," she said.