Probably special unit LEO who just got done with training and needed to pick something up at the store. I have done it myself after instructing on the range. I carry with badge next to gun, but if he was doing PT or something and didn't want to risk damaging his badge he may have left it in his ride.
That was my first thought...
It would have been either that, or a whack job.
I'd lean more to the idea that it was a LEO, but the whack job is a certain possibility, with a decent level of likelihood....
