I remember this case quite well. I know that a lot of people on here are leery of the boyfriend's story, but I've always believed him because it's a story that makes sense. I can tell you as a person with some car knowledge that if you're racing down a street and you immediately change to reverse, that will KILL your transmission, and I do mean KILL it. It was proven that his transmission was, for lack of a better word, dead. People as why she would call him from a payphone instead of just driving home...? First of all, they were planning on meeting up together. So if the boyfriend was at home, why would they have to meet up somewhere? This tells me that the boyfriend must not have been at home at the place that they apparently shared, right? So calling him to cancel plans to meet up and for her just to go ahead and go home makes much more sense. Also, you have to remember their age and the town they lived in. From all the accounts that I've read, it seems that this was a very laid back and pretty peaceful place, so she must not have had much concern for making a phone call from a payphone at night by herself. As far as a detailed description, she's not the only victim that has been able to give such a detailed description. Sometimes fear can heighten a person's senses.
Now with all of that said, I have often wondered in the past if the boyfriend had something to do with it, but indirectly. My thought was that he could have had her possibly followed. Maybe when they met up, he had something planned to kill her, but I just don't think get that feeling that he had anything to do with it.
It was mentioned serial killer Larry Hall had something to do with it. I think it's worth looking at. I found a composite sketch on the left and a photo of Larry Hall on the right. It's certainly possible they might be one and the same.
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As far as a possible connection between the Springfield Three, maybe. It was mentioned that the description of the truck matches a description of a vehicle seen driven by someone matching Suzanne's description, but the vehicle seen was an older model moss green Dodge van, not a truck with a decal in the window, but you never know. I hope something happens with this case.