What to know about the search for 'Today' show host Savannah Guthrie's missing mother

The Arizona sheriff investigating the apparent kidnapping of "Today" co-anchor Savannah Guthrie 's mother said Friday he remains concerned about the 84-year-old's health as her family anxiously waits for proof she is alive, days into the search. "Her conditions, I would imagine, are worsening day by day," Pima County Sheriff Chris Nanos told The Associated Press on Friday. "She requires medication. And I have no way of knowing whether they're getting that medication to her." Guthrie, who has a pacemaker and other heart issues, hasn't been seen since Jan. 31 when she was dropped off by family at her Tucson-area home, authorities say. DNA tests confirmed that blood found on Guthrie's front porch came from her. No suspects or motive have been identified. Purported ransom notes received by news organizations are being taken seriously, the FBI said. At least one note mentioned details like a floodlight at Nancy Guthrie's home and an Apple watch. Here's what to know about the case: Message to kidnapper Savannah Guthrie and her two siblings have spoken in videos posted on social media, urging their mother's captor to contact them. "We are ready to talk. However, we live in a world where voices and images are easily manipulated," Savannah Guthrie said Wednesday, sitting between her brother and sister. "We need to know without a doubt that she is alive and that you have her. We want to hear from you and we are ready to listen." Camron Guthrie reiterated that plea in another video Thursday. "We haven't heard anything directly. We need you to reach out, and we need a way to communicate with you so we can move forward," he said. The sheriff deferred questions to the FBI about whether there have been any responses to the videos. Brooke Brennan from the FBI's Phoenix office said there was no new information to share Friday. The FBI announced a $50,000 reward for credible information about the abduction. Ransom notes taken 'seriously' A ransom note emailed Monday to KOLD-TV in Tucson included information only the kidnapper could have, news anchor Mary Coleman told CNN. "When we saw some of those details, it was clear after a couple of sentences that this might not be a hoax," Coleman said. The note included a demand for money with a deadline set for 5 p.m. Thursday and a second one Monday. Other media organizations were reportedly sent ransom notes. Any decision on whether to fulfill the ransom demands is ultimately up to the family, authorities say. Crime scene in a quiet neighborhood Nancy Guthrie lived alone in the upscale Catalina Foothills neighborhood, where houses are spaced far apart and set back from the street by long driveways, gates and dense desert vegetation. The area appears to have little street lighting at night, making it less likely that security cameras captured helpful footage. Investigators say she was dropped off at home Saturday night by a family member. Four hours later, just before 2 a.m. Sunday, the doorbell camera was disconnected. Guthrie did not have an active subscription so the company was unable to recover any video. The sheriff told the AP that the lack of useful evidence from cameras at the house is unfortunate "because you've got your hopes up." At 2:28 a.m., the app on Guthrie's pacemaker was disconnected from her phone. She was reported missing around noon Sunday when she didn't attend church. Strong mother figure Savannah Guthrie grew up in Tucson, graduated from the University of Arizona and once worked at a television station in the city, where her parents settled in the 1970s. She joined "Today" in 2011. In Wednesday's video, she described her mother as a "loving woman of goodness and light." Her sister, Annie Guthrie, added: "Mamma, If you're listening, we need you to come home. We miss you." ___ Associated Press writers Ed White in Detroit, Jacques Billeaud in Phoenix, and Sejal Govindarao in Tucson, Arizona, contributed to this report.