An undercover California Highway Patrol officer who was attempting to infiltrate a demonstration against police brutality in Oakland pulled a gun on the protesters after he and his partner were outed. About 50 people were marching near Lake Merritt just after 11:30 p.m. Wednesday when some of the demonstrators began calling out two men who were walking with the group," said [news photographer] Michael Short. "Just as we turned up 27th Street, the crowd started yelling at these two guys, saying they were undercover cops," Short said Thursday. "Somebody snatched a hat off the shorter guy's head and he was fumbling around for it. A guy ran up behind him, knocked him down on the ground. The crowd began surging on them. "The other taller guy... as the crowd started surging on them, he pulled out a gun." Chief Browne said the officer also pulled out a badge ... though Short, other members of the media and protesters reported that they did not see a badge. The officers, who Browne said he is not identifying, had been trailing the crowd in an unmarked car and began following on foot. Short said the officers were wearing street clothes and had their faces covered with bandannas. Browne confirmed this and ... said it was common. Several protesters took to Twitter to say that the officers had actually instigated acts of vandalism and were banging on windows alongside others.