This piece, by Julianne Hing, is probably the best piece of analysis I've seen of the Oscar Grant trial. Hing concludes:
But what will always be a matter of contention in any police brutality case, and certainly in this one, is whether the use of force was appropriate for the actual level of threat Grant and his friends posed to the BART cops. If the jury buys the theory that Mehserle intended to pull only his Taser on Grant, does that mean he was within the law when he shot an unarmed man?
That's a tougher legal question than it is a moral one. Because what jurors have also learned during this trial is that police officers have total discretion as to what tool they need to subdue suspects. Moreover, they are allowed to use any kind of force that corresponds to the level of threat they perceive they're under.
So it's difficult to prove cops have been guilty of excessive force and intentional abuse; the only defense a cop needs is that he or she fears life-threatening danger. Mehserle says he feared such danger that night. When I spoke last week with Jack Bryson, whose son Jackie was handcuffed and kneeling next to Grant on the BART platform, Bryson was furious about the trial testimony. "From the very beginning, we have seen total fabrication from every officer who has taken the stand," Bryson told me. He was confident that the prosecution would reveal these cracks in the cops' testimony, but when I asked him if he thought Mehserle would be convicted of murder, Bryson paused. "History is not on our side," he replied.
I think the point about perception is really good, and bears repeating, as we've seen it come up repeatedly in these cases. In the main, if an officer can can demonstrate that he was afraid for his life, he'll walk. How do you know the officer was afraid? Because he says so. It's not important whether Amadou Diallo had a gun or not. What's important is that the cops thought he did.