The ninja disguise is working! 
:smack:
My wife managed a drive-up branch for a few years. Part of the daily routine was that a policeman would escort a staffer with the day’s cash from the main branch in the morning, and another would escort a courier with a bag back to the main branch in the evening. Often, the cop would come in to shmooze and cadge a cup of coffee. That might be what you’re seeing.
Did you check the back seat? He could be having 40 winks at the end of his shift.
Or something else, we used to see a police car show up and park in one of the empty ambulance slots at our station late at night. A few min later his g/f would show up, they would leave after an hour or so. We never bothered to find out what they were up to, probably dinner.
Not alone, he better not. You don’t get out of the back seat of a police car by yourself: you have to be let out.
Hijack: In my home city of Niceville, there was a police officer who had a habit of parking his policemobile just in this shady spot in the woods and taking a nap in the back seat. He did this so much that it got noticed by some of my almost-JD teen-age friends.
One day, a couple of them snuck up on the guy and slammed both back doors.
Some police cruisers aren’t ordered with a partition. In that case, you could just climb into the front seat from the back.
The Akron cop that helped me out last year when I ran out of gas had no partition in his Crown Vic.
The OP didn’t state if there was a partition on the vehicle in question.
Oooh. Maybe he met a co-worker at the bank and they car-pooled?
How far is your nearest Dunkin’ Donuts or Krispy Kreme?
OP Update:
The cop car was there today – with a cop in it. I was running late, so this was at 7:40; I usually pass there before 7:30.
I don’t know If this analogous situation applies, but due to the byzantine rules where I work, the Inspectors aren’t allowed to take their state vehicles home, but often have inspections so early it makes no sense to go to the office first. Rather than reimburse milage for use of personal vehicles, the Agency has authorized contacting local Fire departments (close to the inspector’s home) and using their parking lots for the state vehicles overnight. The Inspectors can drive (or walk) to the Fire Station, get his state vehicle, then go to his 7am inspection. Maybe a cop who lives close by thinks the bank is safe enough to park his cruiser there?
update
Been seeing the cop car, usually empty, most mornings – this morning there were *two * cars, parked do-si-do so the drivers could talk to each other.