Why?

First, some background for my readers beyond the Bay Area. Nineteen months ago, a man was shot and killed by a cop during a brawl at a BART (Bay Area Rapid Transit) station in Oakland. The officer (a BART employee, not an Oakland city policeman) says that he reached for his taser, but mistakenly got his gun instead.

In the heat of the moment, he killed a man who was lying face down on the floor. The action was captured by a number of people with cameras (it happened after the 2008/09 New Year's Eve festivities), and was prominently featured in the news. The victim was black, the cop is white - oops. The black community saw this as a racist action, and proceeded to riot in the streets of downtown Oakland, causing a lot of damage.

Fast forward to last week. The trial ended, and the jury returned a verdict of involuntary manslaughter, which carries a 2-4 year sentence. See news item here. Considering the circumstances, I believe this to be the correct verdict, but the victim's family claims it is too light, and proclaimed as much on TV. This led to yet more rioting in the streets of Oakland and, of course, more damage ensued. (Interesting sidenote: Only ¼ of the 78 people arrested are residents of Oakland - some of them even came from other states!)

My question: Why do people find it necessary to damage the storefronts of businesses that had absolutely nothing to do with it? There is no connection to the incident at all. This chain of events is illogical, unnecessary and, well, tragic. Help me understand - please!