This answers one of the questions I had initially.
It's too bad this wasn't available sooner.
The police officer, Darren Wilson, was responding to a 911 call. This explains why he confronted Brown. It also means that attempting to detain Brown by force was justifiable on the officer's part since a crime had been, or was alleged to have been committed.
There's still the question of exactly how the confrontation unfolded out on the street. Nevertheless, this is certainly supportive of the official police side of the story, and it appears more likely that the shooting might have been justified.