Unsolved Mysteries did a story about a guy who dated women, and all of them mysteriously disappeared afterwards. I think they found one of the women's bodies and he was sent to prison for her murder, but never found the other alleged victims (they were thought to be thrown down mine shafts in the Western states like Nevada, Colorado, Utah or something, but never found). What case is this?

Could it be Robert Weeks? None of his victims were ever found, but he was convicted of two of the murders.

http://unsolvedmysteries.wikia.com/wiki/Robert_Weeks