Officer Michael Daragjati had no idea that the FBI was listening to his phone calls. Otherwise he would probably not have described his arrest and detention of an innocent black New Yorker in the manner he did.

Daragjati boasted to a woman friend that, while on patrol in Staten Island, he had "fried another nigger". It was "no big deal", he added. The FBI, which had been investigating another matter, then tried to work out what had happened.

According to court documents released in New York, Daragjati and his partner had randomly stopped and frisked a black man who had become angry and asked for Daragjati's name and badge number. Daragjati, 32, and with eight years on the force, had no reason to stop the man, and had found nothing illegal. But he arrested him and fabricated an account of him resisting arrest. The man, now referred to in papers only as John Doe because of fears for his safety, spent two nights in jail. He had merely been walking alone through the neighbourhood.

The shocking story has added to a growing sense that there are serious problems of indiscipline and law-breaking in US police forces. Last week the feminist author Naomi Wolf was arrested outside an awards ceremony in Manhattan. She had been advising Occupy Wall Street protesters of their rights to continue demonstrating outside the event. Instead, as she joined the protest, she was carted off to jail in her evening gown. That incident is only the most high-profile of many apparently illegal police actions around the protests. One senior officer, deputy inspector Anthony Bologna, created headlines worldwide when he pepper-sprayed young women behind a police barricade.

A report from the New York Civil Liberties Union recently looked at police use of Taser stun guns in the state, and revealed that in 60% of incidents where they were used, the incident did not meet the recommended criteria for such a weapon. Some cases involved people already handcuffed and 40% involved "at risk" subjects such as children, the elderly or mentally ill. "This disturbing pattern of misuse and abuse endangers lives," said the NYCLU's executive director, Donna Lieberman.

In Los Angeles, officers in the sheriff's department are accused of physically abusing some prison inmates and having sex with others. An internal report, obtained by the Los Angeles Times, revealed allegations that included beating people visiting relatives in jail. In Pittsburgh, there is the case of Jordan Miles, a high-flying high-school student stopped by three plainclothes policemen. Miles, 18 at the time, was walking to his grandmother's house and had no idea who the men were, as they did not identify themselves. He ran, but the officers caught him and beat him so badly that he ended up in hospital. He is undergoing neurological treatment for memory problems and has had to drop out of college.

Yet it was Miles who was charged with aggravated assault – a case that a judge later threw out. His mother, Terez Miles, said: "We are no strangers to police brutality in the city of Pittsburgh, but what they did was terrible and then they lied about it."

In Chicago, Jimmel Cannon, 13, was shot eight times by police who claimed that he had a BB gun in his hand. His family said that he had his hands in the air. In Tucson, Arizona, former marine Jose Guerena was killed by a Swat team on a drugs raid. They found nothing illegal, but Guerena was shot 23 times.

The list goes on. Miami is still dealing with the fallout of the fatal shooting of Raymond Herisse. He had been driving a car out of which police claimed gunshots came. However, it took three days before they produced a weapon. They also confiscated and destroyed the phones of people trying to record the incident.

"There is a widespread, continuing pattern of officers ordering people to stop taking photographs or video in public places, and harassing, detaining and arresting those who fail to comply," said Chris Calabrese, of the American Civil Liberties Union. Campaigners say the spread of camera phones is why so many incidents of brutality are appearing.

In another recorded call, Daragjati complained to a friend: "I could throw somebody a beating, they catch me on camera, and I'm fired." Some activists have taken that to heart. Diop Kamau, a former officer, runs the Florida-based Police Complaint Centre, which investigates allegations of police abuse nationwide. "Police are now facing an onslaught of scrutiny because everyone has a cellphone," he said.

Kamau said that many police departments still had a culture of secrecy and many officers believed that there was little likelihood of punishment even if caught. "The police fill in the blanks. They say what happened and they will be believed," he said.

One weakness is that there is no central organisation for the police, and local departments do not release data on complaints or allegations of abuse. "The problem is that there is an absence of research," said Professor John Liederbach, an expert in American policing at Bowling Green State University in Ohio. As the list of complaints and incidents grows, that might be about to change.