As the urgent search for Nancy Guthrie, the mother of "Today" show host Savannah Guthrie, enters its fifth day, the FBI said it is now jointly investigating the case and has made an arrest in what it called an "imposter" ransom demand.
Nancy Guthrie is believed to have beenabducted from her Arizona homeearly Sunday, authorities said. No suspect or person of interest has been identified in the case, Pima County Sheriff Chris Nanos said during a press briefing on Thursday.
"Right now, we believe Nancy is still out there," Nanos said. "We want her home."
The sheriff said authorities are operating from a position that Nancy Guthrie is alive, and "we're going to continue thinking that way until we find her."
The FBI announced Thursday it is offering a $50,000 reward for information leading to the recovery of Nancy Guthrie and/or the arrest and conviction of anyone involved in her disappearance.
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Nancy Guthrie, 84, was last seen at her home in the Catalina Foothills area, north of Tucson, on Saturday night, according to the Pima County Sheriff's Department. She was dropped off home shortly before 10 p.m. after having dinner with her family, he said. Her family reported her missing on Sunday around noon local time after she failed to show up to church, authorities said.
Nanos provided new details of activity after Nancy Guthrie was last seen. At approximately 1:47 a.m. Sunday, the doorbell camera at her home disconnected and authorities do not have it in their possession, he said.
At 2:12 a.m., the software detected a person on a camera, but there is no video available because there isn't a subscription, he said, adding, "Could that be an animal? I imagine that's possible. We don't know that."
At 2:28, her pacemaker app "shows that it was a disconnect from the phone," he said.
Nanos confirmed Nancy Guthrie's blood was found on her porch. He did not confirm if any cameras were smashed or destroyed around the house, or if there was any forced entry.
There is a possibility her disappearance has "nothing to do with a kidnapping," and it is unclear whether Nancy Guthrie was targeted or not, Nanos said Thursday.
"We cover all angles. We're not going to dismiss something," he said.
Ransom letter being taken seriously; alleged imposter arrested
The sheriff's department has said it is reviewing possible ransom notes as part of the investigation and if they are legitimate.
One letter was sent to several local and national media outlets, Heith Janke, special agent in charge of the FBI's Phoenix office, confirmed on Thursday. The letter made a monetary demand by 5 p.m. Thursday, and if that wasn't met, a second demand for Monday, according to Janke.
That letter also included details on an Apple Watch and a smashed floodlight, according to Janke, who noted those are details that could have been known to the public.
"But that's why we're taking it serious no matter what, and following the leads on that," he said.
Janke said one arrest has been made related to an "imposter ransom demand."
The suspect, Derrick Callella, is accused of demanding Bitcoin from members of the Guthrie family, according to a federal complaint.
Callella allegedly sent a text message to both the daughter and son-in-law of Nancy Guthrie on Wednesday that said, "Did you get the bitcoin were [sic] waiting on our end for the transaction," according to the complaint.
The text messages were sent two days after a local Tucson media outlet received a ransom demand that listed a Bitcoin wallet address to receive the payment, according to the complaint. They were also sent shortly after Nancy Guthrie's childrenpublished a video onlineasking their mother's kidnappers to contact them, the complaint also noted.
Callella allegedly used an application to create a fake phone number to text the family, and the account was tracked to an email associated with him, according to the complaint.
He allegedly admitted to sending the text messages after being read his Miranda rights, according to the complaint.
"When he said that he sent text messages he was trying to see if the family would respond," the complaint stated.
Callella is not linked to the Bitcoin ransom demand, according to the complaint, which charges him transmitting a demand for ransom and intending to abuse, threaten or harass using a telecommunication device.
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Janke issued a warning following Callella's arrest.
"To those imposters who are trying to take advantage and profit from this situation, we will investigate and ensure you are held accountable for your actions," Janke said.
Janke said any action taken on a ransom is ultimately decided by the family.
Savannah Guthrie directly addressed the reports of a ransom letter in a video message with her siblings on Wednesday, saying, "As a family, we are doing everything that we can. We are ready to talk. However, we live in a world where voices and images are easily manipulated. 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. Please reach out to us."
FBI jointly investigating case
The FBI said Thursday it is now jointly investigating the case with the Pima County Sheriff's Department.
The agency is sending additional agents and experts to Pima County to help reinforce efforts on the ground and to aid local investigators, sources told ABC News on Wednesday.
"We are actively reviewing and analyzing information from all digital sources, which includes banks, social media companies, phone companies and any other organizations where a digital footprint could have been captured," Janke said. "All this information provides data points and helps put the picture together."
Nanos said earlier this week that investigators were waiting to get surveillance footage from the home's security cameras from the companies that own them.
A Google spokesperson confirmed to ABC News on Thursday that the company, which is behind Nest home security cameras, is assisting law enforcement in the investigation. The spokesperson declined to elaborate, citing the ongoing investigation.
Savannah Guthrie and her siblings made anemotional pleafor their mother's return in the video message posted to social media on Wednesday.
"Everyone is looking for you, Mommy, everywhere," Savannah Guthrie said in thevideo message. "We will not rest. Your children will not rest until we are together again."
Nancy Guthrie is described as having some physical ailments and limited mobility, but does not have cognitive issues, according to the sheriff. She takes medication that if she doesn't have in 24 hours, "it could be fatal," Nanos said.
"Our mom is our heart and our home," Savannah Guthrie said in the video. "She is 84 years old, her health, her heart is fragile. She lives in constant pain. She is without any medicine. She needs it to survive. She needs it not to suffer."
Janke called on those involved with her disappearance to "do the right thing."
"This is an 84-year-old grandma that needs vital medication for her well-being," he said. "You still have the time to do the right thing before this becomes a worse, much worse scenario for you. Please return Nancy home."
Anyone with information is urged to call 911 or the Pima County Sheriff's Department at 520-351-4900.
As the urgent search for Nancy Guthrie, the mother of "Today" show host Savannah Guthrie, enters its fifth...
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