I also want to know why the uncle was so involved. Maybe he was one of the guys there as well? He seemed to tip off the police about the guns. I don't think Sean did the shooting but you're right that they left out what could have actually happened but I guess that was their case - remove the implication of Sean and focus on the corrupt nature and lack to credibility of the cops that were involved.
Also, that McNelley (?) is a proper twat. Couldn't see the biased right in front of his own eyes and said the case was clear as day regularly, wouldn't offer up any evidence of Sean being the killer. If anything it just added further suspicion of how much he was involved in the corruption as the boss of the main 3 the focus was on.
The police kind of shot themselves in the foot when they messed up with the witnesses and timings (Brown and Sanchez) and the latter's witness ID. They were probably so used to fudging stuff and getting away with it that they didn't realise it would catch up with them at some point. I wonder who the 83,000 dollars was paid to. Such a massive amount to conveniently go missing or not be accounted for...