(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.