If the prosecutor does his job, it really is not hard to see. During the preliminary hearing one of the officers testified that Mehserle made a comment right after the shooting stating" I thought he was going for a gun." I would believe it could be a mistake but given the totality of circumstances, he is guilty of murder in the second degree.
If Mehserle thought Grant was reaching for a gun, lethal force would be an acceptable act. But Mehserle is claiming to have accidently grabbed his gun instead of his taser. My angle would be this given the defenses stance:
Mr. Grant was on his stomach face down. His hands looked to be behind his back. There were 2-3 other officers standing over him. What threat did he pose to Mehserle or his colleagues? This incident is a misuse of force which resulted in death. An accident would be worthy of manslaughter. This was an intentional mistake, not a negligent one given the totality of circumstances. His actions following the shooting and the inconsistent statements even after they had time to come with a story point towards guilt. He will atleast recieve a manslaughter conviction, imo.
this is obviously a short to the point argument. But believe your boy could put together a 20-25 page argument with supporting facts and cases to shit on the defense of Mehserle. This is the type of occasion I want the prosecution to win and serve justice.