By SCOTT WILSON

LOS ANGELES-Police arrested 12 people last night in Hollywood in connection with robberies and vandalism committed by a rampaging mob.

"The incident occurred at around 8:00 p.m. Tuesday," Los Angeles Police Department spokesman Officer Cleo Joseph told ABCNews.com. "We arrested 12 people, 11 for robberies, and one for receiving stolen property."

Joseph said the arrests were made over the course of three hours. A group of young adults allegedly robbed tourists and local businesses in the area, Joseph said. Tuesday night's rampage was unrelated to the Trayvon Martin demonstrations, he added.

LAPD is looking into video surveillance footage from local businesses as they go forward with investigation, he said.

The robberies occurred after a series of protests in Los Angeles, and across the nation in response to the acquittal of George Zimmerman in the Martin killing.

A separate group of individuals broke off from a peaceful march, assaulting onlookers and vandalizing surrounding property, LAPD Police Chief Charlie Beck said in a press conference Monday.

This resulted in the arrests of 14 people, who were charged with the refusal to disperse, though instances of assault and vandalism were reported, Beck said.