Well actually, I don’t think it required prior experience. Speaking for myself, I watch mostly true crime programs on ID Discovery. After a while most ordinary, non-professional observers such as myself, soon learns the various schemes and mistakes murderers make. With the cameras available today, many crimes are nipped in the bud. In this crime, there were none and there were no cell phones in wide use in 1992.
I probably have said this before but it is my opinion that the perp, a sole male, happened to be in communication with Suzie at the Hanover party. Unfortunately she had the unfortunate habit of having relationships with some unsavory individuals. All that the perp needed to do was merely to follow the girls home to the Delmar address.
We can’t be sure but there is a clue with the window shade that Suzie looked out and recognized the perp and/or his vehicle and believed or “trusted” him enough to either let him in or go outside to meet with him. It is highly probable that Sherrill had her bedroom window open (due to paint fumes) and heard the conversation or perhaps an argument and she went outside as well. If the perp was a well developed young male (a given) he could have quickly subdued two small women with plastic tie wraps. Stacy obviously came out later.
For what it is worth, it is my recollection that Cox was arrested for the last time with tie wraps and duct tape in his car. I see nothing that would rule him out.
Alternatively it could have been a police officer.