My preference for a character is going to be the young woman who works in the diner from midnight until 9:00 am. She takes the orders, mixes the drinks and serves the food, that is cooked by a fat Italian guy in back.
Red, if you think that her having a "secret agenda" is a good idea, we can talk about it via PM, otherwise, she can just be a simple waitress that people come to for a decent breakfast at a reasonable price, a late night snack, an insomniac's coffee, whatever. People talk to her. She sees things and hears things.
So yeah, basically a "Key Witness"!