Apparently an officer, who was unloading his vehicle in the police garage, set the rifle on the trunk of a nearby car. Another officer then got in that car, drove off and went to a Starbucks.
The gun, which police say was probably loaded, didn't fall off during the drive. Two people spotted the rifle on the parked car and alerted officers on bikes.
Typically, an officer is either reprimanded or suspended for a day or two when a gun is left unattended.