Unless a witness is able to get a more detailed description of the sniper/sniper's vehicle (or follow him) there's very little the police can do. Once the sniper is allowed to fall into his preplanned escape, which certainly includes evading roadblocks, he simply will not be caught.
This guy(s?) will get nabbed when a neighbor/friend/relative turns him in or when a citizen on the scene disrupts his plan.
Bottom line: these roadblocks are window-dressing, in the same vein as airport security "improvements".