Hypothesis: Shooter has multiple accomplices. One drives a decoy vehicle with no connection to the shooting. A second car serves as a "dump" zone within a block or so of the shooting, where the weapon is dumped. The shooter's initial goal is to get to the "dump car" (a motorcyle would be very effecive for this). The gun unloaded, the shooter then exits the scene via foot or via a third vehicle. He might even have a disguise for his person that would appear to give him reason for being present in the area--EMS, etc.
This scenario serves to give multiple cutouts to further give the shooter a means to escape.