a guy that she had been talking to online for quite some time, you know. maybe she ran away to be with him. >> reporter: a missing person's case was opened, but nothing came of it. aaron and his brother moved in with ralph full-time. but aaron couldn't move on. she had to have left some trail somewhere. barely a teenager, he taught himself every web search engine. looked for years, but found no sign of his mom online. and a terrible suspicion took hold of him, hardened into something like certainty. his mother must be dead. his father must have done it. >> and after that, it became more of, okay, well where would he put her body? >> reporter: he was maybe 13 or 14 when he thought about those old coal mines around walsenburg. did you actually go out and look? >> oh yeah, oh yeah. i went through a lot of those mines myself. >> reporter: alone? >> mm-hmm. >> reporter: you're looking for the remains of your own mother. i can't imagine what that -- >> i can't explain it.