“An unnoticed observer in the house later revealed that their encounter ended in murder, a police report said. Five days afterward, Mr. Aiello’s stepdaughter, Karen Navarra, 67, was discovered by a co-worker in her house with fatal lacerations on her head and neck. She had been wearing a Fitbit fitness tracker, which investigators said showed that her heart rate had spiked significantly around 3:20 p.m. on Sept. 8, when Mr. Aiello was there. Then it recorded her heart rate slowing rapidly, and stopping at 3:28 p.m., about five minutes before Mr. Aiello left the house, the report said.”

Source : Police Use Fitbit Data to Charge 90-Year-Old Man in Stepdaughter’s Killing – The New York Times