San Jose, California, police charged 90-year-old Anthony (Tony) Vincent Aiello in the gruesome death of his 67-year-old stepdaughter after obtaining dramatic health data recorded by her Fitbit Alta HR device.

The stepdaughter, Karen Navarra, was found dead in her house on Thursday, September 13, from multiple deep and instantly incapacitating skull wounds likely inflicted using a small hatchet or axe, according to a police report and autopsy. Her Fitbit data indicated the exact moments those wounds occurred, with her heart rate dramatically spiking then crashing to nothing. The timing of that plummet led to Aiello's arrest.

A co-worker made the initial discovery of Navarra’s murder while checking in on her after she didn’t show up for her job as a pharmacy technician at the Regional Medical Center, where she had worked for 45 years. Police arriving on the scene reported that they found Navarra slouched in a chair at her dining room table, covered in blood and surrounded by blood-splattered surfaces and curtains.

Navarra had a large slash on the right side of her neck and a kitchen knife in her right hand. However, the police quickly judged that the scene was suspicious—and later, unconvincingly staged as a suicide. They noted Navarra’s deep skull wounds and that there was a water bowl on the floor directly below her head, full of dried blood. Drawers in her bedroom and dining room had been yanked open, and other chairs around the dining room table were toppled over. The police called in homicide investigators.

The investigators did an initial assessment, interviewing the co-worker and noting a pizza in the kitchen, some pieces covered in foil and others strewn on the floor. The co-worker told investigators that Navarra was a private person who kept to herself, lived alone with her cats, and didn’t appear to have any romantic partners. She mentioned that Navarra’s parents, who lived somewhere nearby, would likely be the next of kin.

The following day, investigators met with Navarra’s parents, her 92-year-old mother Adele Aiello and stepfather Tony Aiello. Tony quickly explained the pizza in Navarra’s kitchen, saying that he had made it himself and brought it to Navarra on Saturday, September 8, the last day he saw her alive.

Tony told police that he brought the pizza over at about 3pm in the afternoon, at which point he said Navarra was home alone. He told police she let him in and was excited by the pizza delivery. He stayed for about 15 minutes and then left to go back home. He added that he later saw Navarra drive by his house in her car with an unidentified person in the passenger seat. He told police she honked and waved at him as she drove by.

A fitting bit of data

After getting the gory details of the autopsy report, the investigators started working on tracking exactly what happened that Saturday, the last day Navarra was known to be alive. They collected surveillance footage of both Navarra’s home and the Aiellos’ home from around their respective neighborhoods. Remembering that Navarra was also wearing a Fitbit on her left wrist at the time of her death, the investigators also worked to crack into that data. They ended up getting a search warrant for it. Fitbit Director of Brand Protection Jeff Bonham took custody of Navarra’s device and worked on retrieving data on her heart rate and movements from her final days.

Surveillance footage near the Aiello’s house stood in conflict with Tony Aiello saying his stepdaughter drove by with an unidentified passenger. But a security camera facing Navarra’s driveway from a neighbor’s home did capture Tony’s car parked at her house that afternoon. The motion-activated recordings caught glimpses of Tony’s car at Navarra’s house on Saturday, September 8 at 3:12, 3:14, 3:19, 3:21, and 3:33pm. A clip at 3:35 showed the car gone.

Meanwhile, Fitbit’s Bonham got back to the investigators with the health data. He reported that Navarra's device had been connected via Bluetooth to a nearby paired device when police discovered her, and the Fitbit had been reporting data every 15 minutes. The investigators noted that Navarra’s desktop computer was just five to ten feet away from where they found her body in the dining room. Her last recorded movement was on Thursday, September 13, approximately when the coroner removed her body from her home.

Before that, her last movement was on Saturday, September 8, the day Tony dropped off the pizza. It was also the last day the device recorded her heart rate. The Fitbit recorded a “significant” heart rate spike at 3:20pm, and it then rapidly declined. By 3:28—while Tony’s car was still parked in her driveway—her heart had stopped beating, according to the device.

With a warrant to search the Aiellos’ house, the investigators found bloody clothes belonging to Tony. They also found evidence of blood in multiple sinks.

Confronted with all the evidence, Tony Aiello stuck to his original story, saying Navarra was still alive when he left her and that someone else could have been in the house. He explained the blood saying he tended to cut himself a lot. But after the interview, investigators overheard Tony talking to himself while still in the interview room. According to the investigators, he repeatedly said to himself several times, “I’m done.”