her cousin, country singer whitney duncan. >> this is not real. it can't be real. that doesn't happen back in my hometown. >> reporter: right here tonight, those parents who never gave up, now speaking out, only to "20/20." >> i would lay on her bed just trying to feel her again. feel her hand in my hand. >> reporter: their six year journey into the dark underbelly they never knew was just down the road. >> i know my boys. they're drug addicts. they're not murderers. >> reporter: everyone was a suspect. even holly's own brother. >> have you told everything you know about that morning? the trial that made them relive it all. >> boom, boom, boom. he said, i need you to help me bury this body. >> reporter: how did you listen to that testimony? >>> testimony so excruciating. that mother collapsed in the courtroom at one point. good evening. i'm elizabeth vargas. >> i'm david muir. it's a family that really could be any family. your family, a small beautiful town, that mother, a grade school teacher. >> confronted with the shock of finding out someone she had taught in