sort of dance, i told you so and i am sure she's thrilled we got married on her birthday. that would have made her ecstatic. i'm craig melvin. >> and i'm natalie morales. >> and this is "dateline." i fell to the floor. i just remember, like, she's dead, she's dead! and i was so confused. i was like, what's going on? what happened? >> a small texas town, two super close friends, and a summer night in the park. >> they have this lookout, and you could see the harbor bridge lit up. it's really pretty when the stars are out. >> it was the next morning that

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? here's josh mankiewicz with "a texas twist." >> named for the body of christ, corpus christi sits on the texas gulf coast and just east of the bay is a park known for bird watching, and that's what chris seymour was doing there when she came across something very unnatural. >> to me, it just looked like a pile of debris, to be honest. and then he looked, and he said, oh, my god, it's two bodies. >> a crime so shocking that years later they're still talking about it. >> i can't even imagine what was in that person's mind that evoked his violence, his rage. >> two young women. who wanted them dead? and why?

>> it was a true whodunit-type murder. >> and along with who and why was the question of why here? >> this was definitely something that we weren't used to or accustomed to in our town. >> this part of texas isn't exactly ground zero for murder. it's known more for roping, riding, and friday night lights. here life is pretty simple, as are the values its people hold dear, like friendship, family, community. this is where 19-year-old mollie olgin grew up. >> tell me a little bit about what she was like. >> she was really funny. she had a weird sense of humor. always smiling, laughing. she was just a really good person. >> megan olgin was mollie's older sister, just two years apart. they were, says megan, fiercely

competitive. >> she was really smart, which i was always kind of jealous, because math came so easy to her. all the subjects came easy to her. she didn't even have to study, try, nothing. >> mollie also played drums in the high school band, but her friends, brooke ostrom and stephanie chasak say what mollie really loved was cruising down the highway singing along to bands like the spice girls. that's mollie behind the wheel. >> she loved her car a lot. i remember one night when she decided, i'm going to name my car jabbar. and after that, she called her car jabbar macar, and it was the funniest thing for no reason. >> smart, funny, and a car owner, all of which made for one very popular teen. she had a lot of friends? >> yes. >> oh, yeah. >> a lot of friends. >> yeah. >> she never let anybody leave from hanging out with her without giving them a hug and saying "i love you," ever.

>> which was certainly true when it came to the newest member of mollie's unusually large posse of friends, 18-year-old kristene chapa. >> could you tell they really liked each other? >> yeah. >> oh, yeah. >> mollie talked about her a lot. >> she lived in a neighboring town where she was earning a reputation as a softball superstar. >> kristene was a softball icon for this time. >> britney selby was kristene's close friend. >> she was like the comic relief in our little group of friends. >> she says her sense of humor was a perfect match for mollie's. >> mollie definitely brought out kristene's crazy side. it was never a dull moment for those two. >> but for this group of girls, crazy and dull were relative terms. >> we were not the party kids. we never drank or anything like that. we would go to taco bell. we would go to coffee shops, and we would go to parks.

>> which is exactly what mollie and kristene decided to do on a warm summer night back in june of 2012. their destination, violet andrews park. that place seemed safe to you? >> yeah. >> yeah, it did. >> all of the parks were -- i mean, we would go -- >> we would go at night all the time. >> before heading out, the two called britney, asking if she wanted to join them. brit