i told her karlyn's gone. she's gone. >> she was a beautiful young mom doing important work. >> she was an intelligence specialist. >> some of her work was very sensitive. top secret. >> i believe she had top secret clearance. >> when she was found dead, everyone wondered, did her work cost her her life? >> i remember them telling me did she come into a lot of money she couldn't explain? >> maybe she was selling secrets? >> maybe. >> that's like out of a spy novel. >> what about other secrets? the personal kind. >> we knew they were having issues. >> right before they got married she found out that he was cheating. >> but somewhere out there was a stranger keeping secrets too. >> my data guy starts going through her facebook. >> she made reference to firearms in her social media. >> we saw that they were communicating her gas mileage. what a weird thing to do. >> a mystery that would drag on for months. and then, one final secret uncovered by science. >> you start peeling the layers back until the number is vi

karlyn's sister put a recording of her singing inside a teddy bear. you'll never know dear how much i >> we are at this point the constant in her life. we want her to feel protected, loved, everything that i know her mom would have given her. >> that's all for this edition of "dateline. " i'm natalie morales. thank you for watching. >> i'm craig melvin. >> and i'm natalie morales. >> and this is "dateline." i call and her phone went straight to voicemail, over and over and over. i realized something was wrong. >> i got the call that they had found heather's car. >> we pop the trunk, and there's our victim. >> a body of evidence that made no sense. >> she was wearing an oversize mickey mouse shirt. >> she own any mickey mouse clothing? >> no. >> she had long hair. >> and her hair was cut? >> her hair was cut. >> who could be this sick in the head to do this? >> potential suspects would pile up, so why did loved ones distrust the lead detective? >> he was off track right from the beginning. >> we were begging them, take him off the case. >> a case, buil

i told her karlyn's gone.e was an intelligence specialist. >> some of her work was very sensitive. top secret. >> i believe she had top secret clearance. >> when she was found dead, everyone wondered, did her work cost her her life? >> i remember them telling me