(NBC News) — On “Dateline,” Fort Worth investigators desperately search for answers after Carla Walker, a 17-year-old high school student, is kidnapped and murdered following a Valentine’s Day dance.

“Dateline NBC” correspondent Josh Mankiewicz reports on the cutting-edge DNA technology and diligent police work that led detectives to identify her killer.

Here’s a preview:

The day of the dance Rodney had finished his shift at a local gas station, gone home, gotten dressed and was heading over in his mom’s Ford LTD to pick up Carla.

JOSH: She looked like a million dollars?

RODNEY MCCOY: Oh yeah. Definitely. T– she– when she dressed up she did it right. And w– with– with her, it really didn’t take that much.

They drove to dinner and then to the dance. The high school cafeteria was dressed up in pink and red. The theme? Love is a Kaleidoscope. Come on, it was high school.

KRISTI SHELTON: Had a great time. Danced the whole night. I remember Carla and Rodney coming in we were all dancing on the floor together.

Rodney and Carla seemed as in love as two teenagers could be. A couple of months earlier, Rodney had given Carla a promise ring.

RODNEY MCCOY: It meant a lot to me. It meant, “I’m here, I’m yours, and I promise you.”

Back at the Walker house, Carla’s mom and dad were playing dominoes with relatives.

Her big sister, Cindy, and her little brother Jim were watching TV. It got to be 1 a.m.

JIM WALKER: And– I heard a car hitting a curb– And then I heard Rodney’s voice outside yelling, “Mr. Walker, Mr. Walker. Help me.

CINDY: Little bit after that, the front door just pounding. You know, pound, pound, pound, pound, pound. So Jimmy and I both went to the front door together. And opened it. And it was Rodney. And he had– was bleeding from his head down his face. Had blood all over his shirt, just screaming. And I looked over his shoulder, like, “Where’s Carla?” And it’s like, “They’ve got her. They’ve got her. They’ve got her.” And I was like, “Who? Who’s got her?”

You can watch “Dateline: After the Dance” Friday on NBC4 at 9 p.m.