Los Angeles ? An FBI investigation prompted by video footage of a man being punched repeatedly in the face by police has demonstrated anew the power of the Internet sensation of the year, YouTube.com.

In addition to being a monumental time-waster around the office, YouTube could also become a tool for keeping police honest, some say.

This week, a clip on the post-it-yourself video Web site triggered a police-brutality investigation by the FBI. The footage shows the Aug. 11 arrest of alleged gang member William Cardenas, 24. Two Los Angeles officers can be seen holding him down; one punches him several times in the face before they are able to handcuff him.

The Los Angeles Police Department is also investigating the officers’ conduct.

Police Chief William J. Bratton said he found the video to be “disturbing,” but stressed that the 20-second clip amounts to only a fraction of what transpired.

The Los Angeles Times reported Friday that a Superior Court commissioner viewed the video nearly two months ago, heard the officers’ testimony and concluded that their conduct was “more than reasonable” because Cardenas was resisting.

Cop Watch LA, a police watchdog group, posted the video on YouTube, said organizer Joaquin Cienfuegos. Cienfuegos said the video was shot by a neighbor of Cardenas with a cell phone camera. The neighbor gave it to Cardenas’ family, who then gave it to Cop Watch, according to Cienfuegos.

In recent months, videos posted on YouTube have rocked political campaigns, brought fame – or infamy – to previously unknown talents and cast unwanted attention on the gaffes of the famous. YouTube and similar video sites are also increasingly becoming repositories for videos that purport to detail wrongdoing by police.

Such amateur clips help cast a spotlight on police wrongdoing that could otherwise go unreported, said Ramona Ripston, executive director of the ACLU of Southern California.

“Unless we throw light onto activities of government, all activities, you never find out what happened,” Ripston said. “This video is an example.”

Police said Cardenas had been wanted on charges of receiving stolen property. In an arrest report obtained by The Associated Press, the officers said they tried to arrest Cardenas after spotting him on the sidewalk, but Cardenas ran.

The officers caught up to him, tripped him and swarmed over him to apply handcuffs, the report said. In their report, they admitted hitting him repeatedly in the face, saying that he was resisting and that they feared he might grab one of their guns.

Cardenas suffered cuts and bruises on his arms, leg and face, and received stitches on an eyelid. His attorney, B. Kwaku Duren, accused the officers of using excessive force.