Guthrie was driven home from dinner at the home of her other daughter, Annie Guthrie, and her husband Tommaso Cioni, arriving just before 10 p.m.
Her doorbell camera disconnected around 1:47 a.m. the following morning, but authorities were able to recover some video showing a masked, armed suspect at her front door.
At 2:12 a.m., home security software detected a person in front of one of her cameras, but investigators could not obtain video. At 2:28 a.m., her pacemaker app disconnected from her phone.
Last month, 11 weeks into the investigation, the FBI finally received a hair sample obtained from the crime scene after it was sent to a Florida forensics lab to no avail. Experts have said it could take weeks or months for more advanced testing.
"The Pima County Sheriff’s Department continues to work closely with the FBI as investigators follow up on leads, review information, and pursue the facts surrounding this case," the spokesperson said.
Police arrived at Guthrie's home around noon on Feb. 1 after relatives reported her missing. They found the back door propped open, according to public remarks from Savannah Guthrie, and a trail of blood drops near her front door.
Police have not yet identified a masked intruder recorded on her front steps by a Nest doorbell camera. They say he was carrying an Ozark Trail brand hiking backpack, available at Walmart. He was also wearing long sleeves, gloves and a holstered pistol.
Guthrie had just turned 84 on Jan. 27.
There is a combined reward of more than $1.2 million.