What about the woman he was said to be having an affair with? I've read no mention of her..
Why?
I'm assuming this Gambles was similar to the old Kresge stores like we had down in Detroit many years ago. They basically sold a little bit of everything and even had a little pet department with gold fish, parakeets, hamsters, and so on.
Assuming Janet's murderer would have had to of walked through the upper floor of the store to get to the basement and commit the murder, and then walk back through the upper floor to leave the store; it seems unreasonable that nobody seen him/her. According to one of the above news articles: the guy (now retired) who was the Reed City police chief at the time is quoted as saying that who ever murdered Janet was filled with a great deal of anger and rage.
So I guess I would have to agree that her sister's theory that it was someone who had an infatuation with her is incorrect.