Two of the confrontations were caught by amateurs, and the footage from one was posted on YouTube. In each case, the video footage might determine who - civilians or police - will face charges.
Law enforcement officials say the episodes provide yet another example of how the proliferation of cheap digital recording devices could change how situations are investigated and how police are held accountable.
"Digital media can be very compelling and powerful evidence. It can even be overwhelming in the right circumstances," said Jeremy Saland, a former Manhattan prosecutor who works now as a private defense attorney.
The Police Department agrees that video footage can be a valuable tool, and not just in brutality investigations. The department will soon be able to receive video or photos directly from the public, along with text messages to the city's tips hot line.
"That's the world we live in. That's a fact of life. Everybody has a camera," Police Commissioner Raymond Kelly said this week. "Generally speaking, it's helpful."
In the YouTube video shot last Friday, footage of the Critical Mass bike ride appears to contradict a police officer's description of a confrontation. The video shows the officer standing in the street as bikes whiz past. He moves toward a cyclist and violently knocks him to the ground in front of crowds of people.
Afterward, authorities filed a criminal complaint saying the biker, Christopher Long, was arrested because he was obstructing traffic in the heart of Times Square.
The complaint said Long, 29, deliberately steered his bicycle into the officer, causing both of them to fall to the ground. He was charged with attempted assault, resisting arrest and disorderly conduct.
Norman Siegel, a former director of the New York Civil Liberties Union who represents Critical Mass riders, said that a decade ago, conflicting reports usually went in favor of police, not civilians. Juries and judges were almost always more likely to believe the officer.
But video evidence can change that dynamic, Siegel said. "I tell all the protest groups that go out public places to have someone in their group with video camera," he said.
Video doesn't always change the equation, as demonstrated when a California jury acquitted Los Angeles police officers in the videotaped Rodney King beating in 1991.
Footage has made a difference, though, in other cases. In June, four men accused of selling drugs to undercover officers at a Queens bar were cleared after surveillance tapes revealed the officers never bought the drugs. Now, investigators are reviewing the officers' prior cases for signs of misconduct.
For all its advantages, video must still be treated with a degree of skepticism, Saland said, especially because technology makes it easy to doctor footage.
"Just like a live witness, any piece or source of evidence needs to be examined, analyzed and challenged," Saland said. "It is imperative to recognize that a photograph or video shows only one angle at a specific snapshot in time."
After the video footage of the bicycle knockdown emerged, newspapers reported on two others cases caught on tape.
The New York Post showed amateur footage from July 4 that depicted two officers hitting a man on the ground with batons. The criminal compliant said the man, who was drunk, struck the officers and swung an umbrella at them. The video doesn't show the entire incident, and the man has said he wasn't drunk.
The Daily News reported a case in which officers were caught on security footage hitting a man.
The cases are being investigated internally by police and also by the district attorney's office. In the meantime, the officers involved have been stripped of their guns and badges and placed on modified duty.
