It is the most uncomfortable feeling running into a subject while shopping at a store they work at especially when they are no longer under investigation.
They don't know me but I surely know them. I know all about them. And, regardless of the purpose or outcome of the investigation, I feel like I am in a "zone" when standing at the checkout counter directly facing my once subject. It's a chance meeting that is not realized until after I come face to face with the person I can identify in one of my files.
Facing the person who I secretly had to learn all about including where they live, who they live with, finances, and personal information that may or may not be considered for the sake of the investigation is TMI (too much information) when they are just a cashier checking you out at the register. I could go to another register but there is no need to. The "cashier" doesn't know who I am nor will they ever know they were under investigation and by me or for what purpose. I can go through the transaction as if they are somebody I do not know.
There have been times that I have had to interact with my subject while investigating. Subject's who think they are being watched will do their best to hide but when they resurface, because they always do, their antennas are on high alert. They look at everyone and everything around them everywhere they go. It's fun to watch as the investigator because you know what they are hiding. You know why they are constantly looking over their shoulder. Yet, if they suspect they are being watched they rarely know who is watching them.
I rarely go undercover these days but when I do I am unrecognizable from my pictures that are posted on the internet. I lurk in the shadow and keep my distance yet stay close enough to keep my subject within viewing range. I am a spy but cannot completely claim I use a clandestine technique, often.
The former subject was sweet, friendly, personable, and had an innocent nature, not ever knowing they had once been investigated by the person that stood before them at the cash register. It was easy to be friendly back and engage in chit-chat about the weather or the good deal I got on my merchandise. Professionalism is the most important element in a moral situation where light and dark meet within the shadow. I imagine this would not be the last time this investigator and former subject cross paths.