One could also make argument that there is no evidence to suggest the killer was a stranger.
It is mostly because of the cracked window that I think the killer is someone they did not know. I think if someone went to a person's house they knew(especially if they did not call first), then I think they would just get out of the car and go inside the house. Or at least they would be comfortable in getting out of the car. This is why I think a phone call is important to let the person know they are coming over first.
But maybe J.B. Beasley was having a cigarette or the killer had a cigarette when he drove the car later. Who knows. That is why they call it a mystery.
BBM I read in one of the earlier posts that the air conditioner in J.B.'s car was broken and that was why the window was down. J.B. was invited to the party earlier in the day. I can see her going directly there without first calling-especially if she had been there on a previous occasion. I can't help but think that the killer was there waiting for J.B. If he was outside, they wouldn't have had to get out of the car. I have often wondered if J.B. didn't contact him sometime during the night and let him know she would be by later.
I don't think either J.B. or Tracie were smokers.