At the New York Public Library, a small group holding a banner against one of the stone lions was arrested and charged with blocking traffic in the middle of 42nd Street, although video showed they were on the steps, and nowhere near the street.

In another case at the library, a police officer testified that he and three other officers had to carry one protester, Dennis Kyne, by his hands and feet down the library steps. Videotape showed that Mr. Kyne walked down the steps under his own power, and that the officer who testified against him had no role in his arrest. The charges were dismissed; the Manhattan district attorney’s office declined to bring perjury charges against the officer who gave the testimony.

Dozens of complaints were sworn by police officers who said they had witnessed people violating the law on Fulton Street and near Union Square, but later admitted under oath that their only involvement was to process the arrests, and that they had not actually seen the disorderly conduct that was charged.

An assistant to District Attorney Robert M. Morgenthau wrote to the Police Department to stress the importance of officers’ not swearing to things they had not seen for themselves. The prosecutors said the confusion surrounding mass arrests made it hard to bring perjury charges.

The case of Christopher Long and Officer Pogan is shaping up as another example of an official narrative being directly challenged by videotape.

In a criminal court complaint, Officer Pogan wrote that Mr. Long deliberately attacked him with the bike  although the videotape shows Mr. Long veering away from Officer Pogan, who pursues him toward the curb.

The officer said he was knocked to the ground by Mr. Long. Throughout the tape, though, he remains on his feet, even after banging into Mr. Long.