LOS ANGELES -- Arlin Pacheco turned her video camera from the kittens on her porch to the police officers she saw chasing and tackling a neighbor.
The camera was rolling as one officer pressed his knee on the man's neck and punched his face.
That arrest of suspected gang member William Cardenas didn't draw much attention until last week, when Pacheco's video appeared on the YouTube website. Footage of two other arrests quickly followed, and the images fueled an uproar and accusations of police brutality in a city already infamous for the 1991 Rodney King beating.
Amateur videos of police using force on suspects have sparked varying degrees of outrage from California to Philadelphia and Europe after onlookers captured incidents on cameras or video cellphones and posted footage on the Internet.
Some law enforcement officials worry about the effect, arguing that showing only a tiny part of an event can't tell the whole story. They also fear that widespread exposure of such video clips might give officers pause in the future, even when force is justified, and that could put people in danger.
"You know, policing is oftentimes not pretty," Los Angeles Police Chief William Bratton said. "The video, as we've seen from time to time, particularly if you're looking at a slice of it, makes it look even less pretty."
Recent images of an Iranian-American student at the University of California at Los Angeles who was repeatedly shocked with a Taser by campus police have been viewed nearly a million times on YouTube and led to protests and an independent investigation.
Police say the footage was notable for what it left out: The student refused to comply with rules that he show a college identification card or leave the library.
Another amateur video shows an LAPD officer using pepper spray on a handcuffed homeless man who was then left in a closed patrol car.
"A video speaks for itself," said Sherman Austin, 23, who trains a network of amateur videographers who film arrests and post footage on the website CopWatchLA.org. "The camera doesn't lie."
But in the 2005 case of the homeless man, Benjamin Barker, a district attorney's investigation cleared the police officers of wrongdoing.
In the Cardenas case, a court commissioner also found that the officers did nothing wrong because Cardenas was resisting arrest on a felony warrant claiming receipt of stolen property.
Civil rights attorney Connie Rice acknowledged the images may "polarize and politicize police investigations," but she said they also force the LAPD to look inward.
"Without them, there is no pressure at all for police to examine use of force, and they are not policing themselves," said Rice, who was appointed by the Police Commission to examine the LAPD's response to allegations of officer abuse.
Bob Baker, president of the 9,000-member union, the Los Angeles Police Protective League, said police have nothing to hide.
The union applauded a plan announced this week to install digital cameras in some cruisers starting this year. Uncut footage of arrests -- even those requiring force -- will insulate police from undue accusations of brutality, Baker said.
"Putting cameras in cars will give people a full story of what took place," he said.
Chris Biller, a retired LAPD veteran, said the feeling of being constantly watched could put officers and civilians in danger.
"It will cause policemen to hesitate, to look around," said Biller .