Dennis Kyne put up such a fight at a political protest last summer, the arresting officer recalled, it took four police officers to haul him down the steps of the New York Public Library and across Fifth Avenue.
"We picked him up and we carried him while he squirmed and screamed," the officer, Matthew Wohl, testified in December. "I had one of his legs because he was kicking and refusing to walk on his own."
Accused of inciting a riot and resisting arrest, Mr. Kyne was the first of the 1,806 people arrested in New York last summer during the Republican National Convention to take his case to a jury. But one day after Officer Wohl testified, and before the defense called a single witness, the prosecutor abruptly dropped all charges.
During a recess, the defense had brought new information to the prosecutor. A videotape shot by a documentary filmmaker showed Mr. Kyne agitated but plainly walking under his own power down the library steps, contradicting the vivid account of Officer Wohl, who was nowhere to be seen in the pictures. Nor was the officer seen taking part in the arrests of four other people at the library against whom he signed complaints.
A sprawling body of visual evidence, made possible by inexpensive, lightweight cameras in the hands of private citizens, volunteer observers and the police themselves, has shifted the debate over precisely what happened on the streets during the week of the convention.
For Mr. Kyne and 400 others arrested that week, video recordings provided evidence that they had not committed a crime or that the charges against them could not be proved, according to defense lawyers and prosecutors.
Among them was Alexander Dunlop, who said he was arrested while going to pick up sushi.
Last week, he discovered that there were two versions of the same police tape: the one that was to be used as evidence in his trial had been edited at two spots, removing images that showed Mr. Dunlop behaving peacefully. When a volunteer film archivist found a more complete version of the tape and gave it to Mr. Dunlop's lawyer, prosecutors immediately dropped the charges and said that a technician had cut the material by mistake.
Seven months after the convention at Madison Square Garden, criminal charges have fallen against all but a handful of people arrested that week. Of the 1,670 cases that have run their full course, 91 percent ended with the charges dismissed or with a verdict of not guilty after trial. Many were dropped without any finding of wrongdoing, but also without any serious inquiry into the circumstances of the arrests, with the Manhattan district attorney's office agreeing that the cases should be "adjourned in contemplation of dismissal."
So far, 162 defendants have either pleaded guilty or were convicted after trial, and videotapes that bolstered the prosecution's case played a role in at least some of those cases, although prosecutors could not provide details.
Besides offering little support or actually undercutting the prosecution of most of the people arrested, the videotapes also highlight another substantial piece of the historical record: the Police Department's tactics in controlling the demonstrations, parades and rallies of hundreds of thousands of people were largely free of explicit violence.
Throughout the convention week and afterward, Mayor Michael R. Bloomberg said that the police issued clear warnings about blocking streets or sidewalks, and that officers moved to arrest only those who defied them. In the view of many activists - and of many people who maintain that they were passers-by and were swept into dragnets indiscriminately thrown over large groups - the police strategy appeared to be designed to sweep them off the streets on technical grounds as a show of force.
"The police develop a narrative, the defendant has a different story, and the question becomes, how do you resolve it?" said Eileen Clancy, a member of I-Witness Video, a project that assembled hundreds of videotapes shot during the convention by volunteers for use by defense lawyers.
Paul J. Browne, a police spokesman, said that videotapes often do not show the full sequence of events, and that the public should not rush to criticize officers simply because their recollections of events are not consistent with a single videotape. The Manhattan district attorney's office is reviewing the testimony of Officer Wohl at the request of Lewis B. Oliver Jr., the lawyer who represented Mr. Kyne in his arrest at the library.
The Police Department maintains that much of the videotape that has surfaced since the convention captured what Mr. Browne called the department's professional handling of the protests and parades. "My guess is that people who saw the police restraint admired it," he said.
Video is a useful source of evidence, but not an easy one to manage, because of the difficulties in finding a fleeting image in hundreds of hours of tape. Moreover, many of the tapes lack index and time markings, so cuts in the tape are not immediately apparent.
That was a problem in the case of Mr. Dunlop, who learned that his tape had been altered only after Ms. Clancy found another version of the same tape. Mr. Dunlop had been accused of pushing his bicycle into a line of police officers on the Lower East Side and of resisting arrest, but the deleted parts of the tape show him calmly approaching the police line, and later submitting to arrest without apparent incident.
A spokeswoman for the district attorney, Barbara Thompson, said the material had been cut by a technician in the prosecutor's office. "It was our mistake," she said. "The assistant district attorney wanted to include that portion" because she initially believed that it supported the charges against Mr. Dunlop. Later, however, the arresting officer, who does not appear on the video, was no longer sure of the specifics in the complaint against Mr. Dunlop.
In what appeared to be the most violent incident at the convention protests, video shot by news reporters captured the beating of a man on a motorcycle - a police officer in plainclothes - and led to the arrest of one of those involved, Jamal Holiday. After eight months in jail, he pleaded guilty last month to attempted assault, a low-level felony that will be further reduced if he completes probation. His lawyer, Elsie Chandler of the Neighborhood Defender Service of Harlem, said that videos had led to his arrest, but also provided support for his claim that he did not realize the man on the motorcycle was a police officer, reducing the severity of the offense.
Mr. Browne, the police spokesman, said that despite many civilians with cameras who were nearby when the officer was attacked, none of the material was turned over to police trying to identify the assailants. Footage from a freelance journalist led police to Mr. Holiday, he said.
In the bulk of the 400 cases that were dismissed based on videotapes, most involved arrests at three places - 16th Street near Union Square, 17th Street near Union Square and on Fulton Street - where police officers and civilians taped the gatherings, said Martin R. Stolar, the president of the New York City chapter of the National Lawyers Guild. Those tapes showed that the demonstrators had followed the instructions of senior officers to walk down those streets, only to have another official order their arrests.
Ms. Thompson of the district attorney's office said, "We looked at videos from a variety of sources, and in a number of cases, we have moved to dismiss."
Copyright 2005 The New York Times Company