like the corner store by myself. >> and then that progressed to school? >> yes. >> reporter: fred couch admitted allowing ethan to drive, but both parents say they didn't >> have you ever seen ethan drink as we sit here today? >> i don't remember ever seeing him drink. >> reporter: maybe not, but she definitely saw him drunk. fatal crash, 15-year-old ethan

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>> why didn't you ask him where he got it? to try to stop it from happening again? >> i don't know. >> reporter: these attorneys say ethan couch, who wasn't even old enough to drive, was violating as many five laws that night. >> five violations of the law and nothing's done by tonya. >> reporter: well, not quite nothing. tonya does admit to concocting a story with ethan to keep her husband in the dark about the more criminal details of that

>>> once again, matt gutman and "20/20." >> reporter: this is the scene most people imagine when they think of puerto vallarta, mexico. but it was here, in this gritty $80 a month apartment building where ethan and tonya couch's mexican vacation came to an abrupt end. a neighbor snapping this photo of ethan, cuffed and being led out by authorities. his black hair and goatee so who ambled into court just two years ago. ethan and tonya had been on the