Murder victim's Fitbit leads to arrest of 90-year-old stepfather, who cops say used small hatchet or ax

A murder victim's Fitbit led investigators to her 90-year-old stepfather, who cops say brutally killed her with a small hatchet or an ax.

California cops say Tony Aiello murdered 67-year-old Karen Navarra in her home on Sept. 8 and tried to stage the bloody scene as a suicide. However, officials said her wounds could not have been self-inflicted.

Aiello, who is married to Navarra's mother, said he brought pizza to her San Jose home on the day of her murder and stayed 15 minutes. However, surveillance cameras showed his car at Navarra's home at the same time that her Fitbit Alta showed a "significant spike" in her heart rate followed by a "rapid slowing," according to a police statement of facts obtained by the Daily News. The Fitbit showed that Navarra's heart rate stopped at 3:28 p.m.

"After explaining the abilities of the Fitbit to record time, physical movement, and heart rate data, he was informed that the victim was deceased prior to his leaving the house," the document read. "Aiello stated that could not be true because she had walked him to the door when he left the residence."

Photo: San Jose Police Department

Navarra's body was found in her home on Sept. 13, five days after Aiello's visit, after she failed to show up for work. She was found "slouched" in a chair at her dining room table.

She was found with a "gaping laceration" on her neck and wounds on the top of her head, according to police. A large kitchen knife was found in Navarra's right hand.

Aiello suggested to cops that someone else might have been in the house when Navarra was killed, but they had found two shirts with blood spatter in the clothes hamper in his garage. He said he might have cut his hand and shaken it while he was wearing those shirts.

He was arrested on suspicion of murder.