(NBC News) — Tonight on “Dateline,” investigators desperately search for a killer after Florida teacher Denise Hallowell is found murdered in her own home.

Friday’s all-new episode examines the Hallowell family’s tumultuous past and features an exclusive interview with Denise’s son and insiders close to the case.

Here is a preview of Dennis Murphy’s report:

The pleasant home on the lake had become a house of horrors. Denise Hollowell: found murdered in her own bed. Her 17-year-old son Carlos reported the macabre discovery.

The Citrus County Sheriff threw everything he had into the search for the woman’s killer.

SHERIFF PRENDERGAST: We deployed not only air, land, and water. We put our canine units out there. And we saturated our areas of the county.

Neighbor and good friend Amy Alford heard the thump of helicopters overhead that July evening. What in the world?

AMY ALFORD: My other neighbor down the road called me and she said the driveway was lined with sheriff’s cars and then she said there was a forensic unit there. And then that really worried me.

And then she learned: her friend was gone.

AMY ALFORD: I felt my knees buckle, and I had to hold onto the post. And it was just a blur after that. We always planned to be– grow old together at the lake. That didn’t happen.

Now on that humid July evening, in the horror of that bedroom where Carlos had found his mother attacked.

Their happy lives were utterly destroyed.

And a murder investigation– an urgent one– was up and running.

Watch “Dateline: Horror at the Lake” on NBC4 at 9 p.m.

About ‘Dateline’

“Dateline NBC” is the longest-running series in NBC primetime history and is in its 30th season. Dateline is anchored by Lester Holt and features correspondents Andrea Canning, Josh Mankiewicz, Natalie Morales, Keith Morrison and Dennis Murphy.

Dateline is the #1 Friday newsmagazine and reaches more than 17 million people every week through its broadcast, and millions more through its social media platforms and podcasts.

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.