From the story Miller was the DD that night and the gun was just in the backseat.
Also, from the report it said the victim's car at one point left the area, came back and parked and turned their lights off. IN another report the victim's car says they did that because they were waiting for their food. . I can understand the potential paranoia that this all can cause. Not excusing it, as it seems like it was mostly self-inflicted, but I can see the situation in my mind and how it would be difficult to navigate.