@3, 7, 10: I concur.
@2: The gun had been purchased by a sheriff's deputy nearly three years previously. He had shortly thereafter sold it to another guy. There's not a very good paper trail because the gun lobby makes it so most gun sales aren't reported, and those that are cannot legally be digitized because of MUH FREEDUMBS. (source
Think about it though. If the cops were gonna murder a guy on the street and later plant a gun at the scene to cover it up, why would they use a gun that had been registered to a police officer? They have access to plenty of guns recovered from crime scenes and felons, including some that have been modified so as to be practically untraceable. Why not use one of THOSE? You're assuming that the police are not only evil, but cartoonishly so.
@8: "Follow their instructions as Taylor did: get shot dead."
If you actually watch the footage, Taylor can clearly be seen to dive back into the car, at which point he is shot. He wasn't following their instructions; he was reaching around inside the vehicle, and they already knew he had a firearm with him, and they made the very reasonable interpretation that he was reaching for a gun.