shauna tiaffay hit the jackpot in las vegas. a handsome husband, an adorable daughter and a good job. but there is a dark side to sin city. sadly, the beautiful cocktail waitress became its victim. in cases like this one, the husband is often a suspect but the crime scene was telling investigators something else. and they got a hot tip. but like so many things in vegas, nothing was as it seemed. here's keith morrison with "under a full moon." >> reporter: she was finished now. tired, wrung out. must have been as she walked away from the incessantly ' chirping machinery and the bleary eyes of the gamblers on holiday from real life who'd called out for her again and again and again. outside in the night, a full moon bathed the great houses of delight and sin in an unaccustomed shade of pale. it was september 29, 2012. at precisely 3:00 in the morning, in a back room of the palms casino, the cocktail waitress named shauna tiaffay inserted her time card in the stamping machine, and set out to break a little rule. shauna had parked h

. >> reporter: shauna tiaffay, loving mom by day, vegas cocktail waitress by night. >> i was at one ofd i saw her walk by. every single head turned. >> it was after her shift that they found her, the victim of a

paula plans to make sure the daughter of shauna tiaffay never forgets. >> we talk about her mom, and how much she loved her, and what we think her mom would want for her now. >> that's all for this edition of "dateline." i'm craig melvin. thank you for watching. >>> i'm craig melvin. >> and i'm natalie morales. >> and this is "dateline." >>> i fell to the floor. i don't remember anything. >> she's dead, she's dead. and i was so confused. i was saying what's going on? what happened? >> reporter: a small texas town. two super close friends and a summer night in the park. >> they have this lookout you could seat harbor bridge lit up. it's really pretty when the stars are out. >> reporter: 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 mouth and hands. >> reporter: a mystifying scene. >> the only thing we have -- >> reporter: dna would point one way. a bombshell message would point to another. >> i looked at the letter. >> takes a special mind that wants to do something like that. >> reporter: to crack