>> shannon who had been angry at ralph for not protecting her mother, read the letter and began to have thoughts that were much more disturbing. >> i didn't get through more than a page and a half and i threw it, and i said, this is bull [ bleep ]. i said, this is the worst -- i could barely stomach to finish it. >> and aaron, shannon's ex-husband, ralph's son? aaron went to a very dark place indeed. oh, you have no idea. you were 11 years old when your mother disappeared. >> yes. >> coming up, secrets in the basement. >> i had been going through some of my dad's stuff in the basement and found a box of stuff that supposedly she had taken with her. >> when "dateline" continues. how do i check my credit score? credit karma. don't worry, it's free.