A doorbell camera was disconnected from Nancy Guthrie’s home on the night she was kidnapped, police said Thursday, depriving investigators of crucial evidence as they search for the mother of “Today” show anchor Savannah Guthrie.

Authorities in Pima County, Arizona, said at a news conference Thursday that they still had no suspects in the abduction of Nancy Guthrie, 84, more than four days after she was taken from her home near Tucson. They confirmed blood found on Guthrie’s front porch was hers.

The new details came a day after Savannah Guthrie and her siblings released an emotional video, in which they said they were ready to listen to ransom offers but first would need proof that their mom was still alive. Heith Janke, the special agent in charge of the FBI’s Phoenix office, said that agents were reviewing purported ransom notes that had been sent to several news outlets, which demanded a payment by Thursday night. Chris Nanos, the Pima County sheriff, has told the New York Times that Nancy Guthrie had dinner at the home of her older daughter, Annie, and son-in-law, Tommaso Cioni, and that Cioni took her home around 9:50 p.m. Saturday.

Nanos said Thursday that a doorbell camera at Guthrie’s home had been disconnected at 1:47 a.m. Sunday and removed, adding that authorities do not know where the device is. At 2:12 a.m., a camera on Guthrie’s property detected motion, but no video was recorded, the sheriff said. Then, at 2:28 a.m., Guthrie’s pacemaker disconnected from her cellphone, which was later found at the house, suggesting that she may have been taken around that time.