The FBI said it will investigate the police beating of a suspect that has became one of the most widely viewed postings on the popular Web site YouTube. The incident occurred in August, when Los Angeles police officers spotted William Cardenas, 23, a suspected gang member wanted in connection with a robbery. The officers chased Cardenas and tripped him up. In a 20-second video shot by a bystander, one officer is seen putting his knee on Cardenas' throat as another punches Cardenas repeatedly in the face. Police say Cardenas was resisting arrest and reaching for their guns, justifying the use of force. The video was first sent to a police watchdog organization and later posted on YouTube. Civil liberties groups said the incident shows the need for stronger oversight of police. "YouTube," said ACLU spokeswoman Ramona Ripston, "is not an acceptable substitute for accountability."