When a Wisconsin man’s girlfriend was found dead in a farm field, Brown County detectives believed he was the prime suspect.

Doug Detrie was arrested days after Nicole VanderHeyden, a 31-year-old substitute teacher, was bludgeoned to death in May 2015. VanderHeyden, a mother of three, was killed 118 feet from the front door of her Ledgeview home.

But cops discovered Detrie had an unlikely alibi: His FitBit activity tracker.

Now ‘48 Hours’ will explore the high-tech whodunit in an episode that features Daily Beast reporter Kate Briquelet, who is interviewed by attorney and Emmy Award-winning CBS correspondent Erin Moriarty.

The episode, titled “The FitBit Alibi,” airs Saturday, March 24, at 10 p.m. ET/PT on CBS.

George Burch, a Virginia felon who moved north for a fresh start, encountered Green Bay cops just weeks after VanderHeyden died. At the time, police suspected Burch was involved in a suspicious vehicle fire with his friend’s Chevy Blazer.

While Burch was never charged, he allowed cops to search his phone to corroborate his movements the night of the accident. That phone data—which was stored in a police database—would later prove incriminating after a state crime lab matched Burch’s DNA with swabs taken from VanderHeyden’s body.

The Dashboard data—which tracked Burch’s movements using GPS, Wi-Fi and cell towers—linked him to multiple crime scenes. Police say Burch was outside VanderHeyden’s home for nearly an hour, before driving to a Bellevue farm field to dump her body and tossing her clothes onto a highway on-ramp.

Still, Burch claimed he had an explanation for his whereabouts.

The felon, nicknamed “Big Country,” claimed Detrie was the real killer. And, at a trial covered by The Daily Beast, Burch’s lawyers painted a picture of Detrie as ne'er-do-well boyfriend who had a motive of his own.