20 minute gun battle erupts on Oakland freeway

So, the cops got into a fierce gun battle with some 45-year old white guy who was armed to the teeth and wearing a flak vest, and eventually subdued the gunmen (by shooting him several times). Even though they had the perpetrator in custody (he is alive and well by all accounts), they still closed a major freeway for an entire weekend day to collect evidence.
Interestingly, after police murdered Oscar Grant at the Fruitvale BART station, they let an entire train full of witnesses leave the station, minus some of their cameras and cell phones.
I wonder why they were more concerned about securing the crime scene and collecting evidence when the victim of an officer-related shooting was white....