they found them. >> i could see two girls laying there. it was horrifying. there was duct tape on their mouths, on their hands. >> a mystifying scene. >> the only thing we have are cigarette butts and suspicion. >> dna would point one way. >> he's like, serge, you've got to take a look at this. >> a bombshell message would point another. >> i read the letter and immediately knew this was something very important. >> a twisted trail leading to a sinister suspect. >> it takes a special kind of mind that wants to do something like that. >> to crack a case this convoluted, it might just take a miracle. >> that was extraordinary. >> i just couldn't believe it. welcome to "dateline. " two young women were discovered in a park bound and gagged. both were sexually assaulted and shot in the head. one died, but the other miraculously was still alive. some wondered, could a secret relationship have been the motive for murder?