Mollie's Fitbit has been the story from the beginning, particularly heart rate - as it most likely corresponds to the exact times that she was most threatened. This provides a timeline of her abduction, assault and murder.
"While details about the leads remain scarce, there is one new kind of data that might end up playing an important role: The Iowa law enforcement agencies have been working with the FBI to use her Fitbit and social media data to look for clues. They’ve been tight-lipped about what information they’re using, but Rahn said they’re trying to find any information that’s relevant to the case.
“We’re trying to use all avenues and techniques to locate Mollie, including any devices she might have, such as the Fitbit, as well as social media outlets,” he told Runner’s World by phone.
In Iowa, law enforcement agencies can use personal data from devices based on family consent, search warrants, and subpoenas. Most other states allow law enforcement officials to use data based on consent and search warrants as well, while some restrict using subpoenas to obtain information. The FBI declined to comment on “specific tools or techniques utilized in criminal investigations,” including this case.
But this isn’t the first time where law enforcement agencies and forensics teams have used smart device data to gain insight on things like GPS locations, heart rate data, steps, and other kinds of activity."
Mollie Tibbetts Disappearance - Fitbit Data in Investigations