Wilson was also allowed to drive himself away from the crime scene.
How did he drive away? His vehicle was there for hours while the criminal investigation unit documented the crime scene? Did he use someone else’s vehicle? Maybe he left because of the numerous death threats from the locals.
The GJ materials answer that question. He felt threatened at the location, and his supervisor gave him another venicle (the supervisor's police vehicle) and told him to go to the police station.
This was not a regular investigation where the police personnel feel safe and secure - it was nearly a riot scene, with hundreds of residents standing around, shouting insults. There were shots fired near the scene; there were people running into the scene across the yellow tape. This is why crime scene techs had to cut their work short. For example, most of the evidence was not photographed before collecting - the rioters made sure that it can't be done. Now they are complaining that the police haven't done everything by the book...