(NBC News) — Thursday on an all-new “Dateline,” young pregnant mother Bethany Decker goes missing in Virginia, her family embarks on a frantic search, but the case eventually goes cold.

Years later, investigators speak with a woman who tells a harrowing story and may hold the key to solving the case.

Here is a preview of Keith Morrison’s report:

It was a kind of hell, that awful time of unknowing after Bethany vanished. Kim Nelson is Bethany’s mother.

KIM: I can’t even count how many flyers I passed out.

Her family knew it was bad — of course they did — but they would not, could not, stop searching.

Here are Kim and her husband on NBC station WRC.

KIM: I’m praying and I have faith that she’s safe.

They got the whole country talking about Bethany.

SAVANNAH: A young pregnant mother has gone missing.

ASHLEY: It kind of just sank in my chest. Like I just steadily got this cold pit and it just got worse and worse, as I like started realizing something, something’s really wrong. But, that can’t, that only happens on TV, that couldn’t happen here.

Detectives, meanwhile, occupied themselves with hard realities.

To them, the facts said, “homicide.”

Watch “Dateline: Bethany Vanished,” Thursday at 10:20 p.m. on NBC4.

About ‘Dateline’

“Dateline NBC” is the longest-running series in NBC primetime history and is in its 32nd season. Dateline is anchored by Lester Holt and features correspondents Andrea Canning, Josh Mankiewicz, Keith Morrison and Dennis Murphy.

The stories range from compelling mysteries to powerful documentaries and in-depth investigations. When major news breaks, they go to the scene, putting the pieces together to bring the viewer the full picture. And in every story they tell, they help the real people who lived the events share their journeys with the viewer.