hincapie never went home again. for more than two decades, his mother maria has made the same two-hour journey every other week since her son was sent away. it's been very hard because it's been 24 years, 24 birthdays, 24 christmas. lester holt (voiceover): they say their visits are heartbreaking for both of them. how? how you've been able to hold on all these years? it's too many years don't cry, mommy. don't cry. lester holt (voiceover): but maria says she's been crying out, pleading for anyone to listen since that very first day her ordeal began. i wanted to scream to the world and tell the world, my son is not guilty. please help me. lester holt (voiceover): little did she know help was on the way. i love you, ok? andrea canning (voiceover): coming up, a new witness could reveal critical information about the night of the crime. but will he talk? he was shaking. he was visibly nervous. he started crying. andrea canning (voiceover): when "dateline" continues. looking for extra hydration. now there's blink neutral