(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 WFLA at 9 p.m.