YouTube video footage featuring a group of police officers beating a suspect, whose sister says is mentally ill, is being investigated by authorities in a Central California city, officials said on Tuesday.The suspect, identified as 28-year-old Jose Velasco, had been assaulting his mother on a city street in Salinas, about 110 miles south of San Francisco, when officers used batons and Tasers to gain control of the situation, the police chief said.However the video clip shows that the two police officers hit Velasco on his head, legs, hands and back. Three more officers arrived on scene, with one jumping in to hit Velasco and two pinning him down, the one-minute-42-second video showed.Officials said police were called to a report of Velasco assaulting his mother on the pavement and running into traffic on Friday. "As the officers tried to get Velasco off of his mother by pulling him away, Velasco began to violently resist and attacked the officers," the department said in a statement.After the attack, Velascotarget="_blank"'>'My poor brother. He is mentally ill and the cops had no right to keep hitting him he was already on the floor,' she posted in the comments section beneath the YouTube clip.