Follow-up
Late follow-up but I read through the website that Traybone started posting on, and the brother of Cynthia posted a couple of times:
drallegro
Cynthia's Brother
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Hello, I am Cynthia's brother Dan. I have been trying to find out what happened to my little sister for twenty-four years. I have good reason to believe she was killed by a Charles Rentschler who is currently in prison in Missouri for another murder. There was never any mention of the boyfriend. I think his name, or the name he was using, was David Griswald. They left Kansas City, supposedly going to St. Louis to buy drugs. They were never heard from again and a body has never been found. I was very close to my sister and know she would never have disappeared on her own. I appreciate your interest in the case and would welcome any help. Thanks.
I wish I knew something else that might be helpful. I had held out hope for a long time that somehow she might be alive, but I'm sure she is not. There are descriptions on the internet that cover dental work, broken bones, and even her tatoo. I wish the missing person's unit of the Kansas City police would send someone to interview Rentchler who is in a prison near St. Louis, but they tell me they don't have the funding to cover such a trip. I'm sure that he either killed her himself or knows who did. I live in Southern California.
Even after all these years, there is not a day that goes by when I don't think of her.