Fitbit data helps lead to arrest of 90-year-old man in stepdaughter’s death

San Jose police officers found Karen Navarra with a gaping laceration to her neck and wounds on the top of her head. In her right hand, was a large kitchen knife.

Her death had been staged to appear like a suicide.

But the Fitbit on her left wrist led police to a murder suspect. The data on the device showed a spike in Navarra’s heart rate at 3:20 p.m. on Sept. 8, followed by a rapid slowing. It ceased registering heart rate data eight minutes later.

Based on video footage and the information from the Fitbit, police arrested Navarra’s stepfather, Anthony Aiello, according to a statement of facts provided by police to the Santa Clara County district attorney’s office.

Last week, Aiello was formally charged with murder with personal use of a deadly weapon, according to prosecutors.

A coworker found Navarra’s body on Sept. 13, when she went to check up on her after the 68-year-old failed to show up at work.

It did not take long for a coroner’s investigator to determine that Navarra’s multiple skull fractures “were inconsistent with being self-inflicted or accidental,” San Jose police Det. Brian Meeker wrote in the statement.

“Based on the totality of the circumstances and information received … detectives believed the homicide of victim Karen Navarra was staged to appear as though it was a suicide,” Meeker stated.

When police spoke with Aiello, who is married to Navarra’s mother, he said he last saw his stepdaughter on Sept. 8. He told police he had dropped off homemade pizza and biscotti for her around 3 p.m.

Aiello told police he stayed about 15 minutes, before driving back to his house. Later that same day, he told police, he spotted Navarra driving by his home. But available video footage never showed Navarra’s car pass by.

Police applied for a search warrant related to the Fitbit Alta HR, seeking information associated with Navarra’s heart rate and movement. The Fitbit had communicated with its paired device and was reporting data every 15 minutes.

The Fitbit stopped registering heart rate data at precisely 3:28 p.m.

Video footage showed Aiello’s car had been parked in the driveway of Navarra’s home from 3:12 p.m. to at least 3:33 p.m., according to the statement.

San Jose police arrested Aiello and took him to the department’s homicide unit for an interview. During that time, another team searched Aiello’s home, where they found clothing with reddish brown stains that tested “presumptive positive” for blood.

Detectives confronted Aiello about the Fitbit data and told him that Navarra died before he left the house, according to the statement. Aiello denied he was there when she was killed and suggested someone else might have been in the home.

After detectives left the room, Meeker said, Aiello could be heard talking to himself.

“Among other things, he repeated the statement, ‘I’m done,’ a number of times,” Meeker said.

brittny.mejia@latimes.com

Twitter: @Brittny_Mejia