>> reporter: but then john richter, the cold case detective, has a white-hot idea., to autopsy matt leili's hard drive, hoping newly available technology will exhume any evidence buried inside the computer. >> oftentimes in my cold cases, i send off clothing, you know. so you might get a dna hit on some clothing that you didn't prior. well, in this case in particular, it was computers. it was the forensic stuff that i decided, you know, let's get a new, fresh look at the computers and the forensics. >> reporter: two weeks later detective ford casually drops the report off at richter's desk. >> and i look at it and i see the word, deleted. and i said, "no, these video files are deleted." he's, like, oh, absolutely. it was all deleted. >> reporter: now the evidence is clear. this was no accident. somebody intentionally deleted security camera video from the precise hours when nique had left -- or been taken -- from the house. the difference between the word "deleted" and "corrupted" for you is what? >> "deleted," to me, means it was deleted by a person. somebody went

richter scale. then a huge tsunami crashing up the coast. it was like watching a disaster movie, this one horribly real. and johnry's son zach was now right in the middle of it. >> what did you think? >> unreal. this can't be happening. are you sure it's where zach is? are you sure it's in the same region? we were looking at maps, and everything was pointing to, yeah, it's exactly where zach is. >> we just prayed. >> enormous waves you see here were hitting noda and kuji, the towns where zach and georgia were teaching. the frantic calls began, to no avail. >> what happened when you tried his phone? >> it would say all circuits are busy and you'd get a busy signal. >> then the minutes went by. >> uh-huh. >> then an hour and two hours. what did that feel like? >> hell. >> as a parent, you never think, oh, my child has been killed. you don't think that. you just wait. you just wait and pray for the best. >> remember, zach had wanted to come home months earlier, but terry and john had encouraged him to stay, to live up to his commitment. >> how much did you beat yourself up about that? >> i did. >> seemed right then