Authorities believe two ransom notes addressed to Nancy Guthrie's family — including a note that said she had died — were likely sent by the person or group of people who abducted her, according to investigators familiar with the case. Investigators believe that the same person or people sent both notes and that both were likely sent from the same computer IP address.

The first note demanded millions in bitcoin for Nancy Guthrie's release. In the second note, sent a few days later, the apparent abductors revealed that Nancy Guthrie had died. The note indicated that they did not mean for her to die, according to sources who reviewed the notes.

Her daughter, "Today" show co-host  Savannah Guthrie, said in an interview with NBC in March that the family believes the two notes are authentic. 

"There are a lot of different notes, I think, that came, and I think most of them — it's my understanding — are not real, and I didn't see them," she said. "But I believe the two notes that we received, that we responded to, I tend to believe those are real."

The first note, sent on Feb. 2, one day after Nancy Guthrie, 84, was reported missing from her home in Tucson, Arizona, was sent to three media outlets — two local news stations and TMZ — via their online tiplines. That note gave highly specific details about Guthrie's home, including that an Apple Watch with a white band was on the floor of her bedroom and that her back porch light was broken, according to investigators. The note was addressed to Savannah Guthrie, according to multiple sources familiar with the note.

The second note was sent on Feb. 6 and was similar in language and style but did not make any demands, according to sources who reviewed both notes.

Savannah Guthrie and her siblings publicly addressed her mother's kidnappers in an Instagram video posted after the second note was sent.

"We received your message and we understand," Savannah Guthrie said in the video. "We beg you now to return our mother to us so that we can celebrate with her. This is the only way we will have peace. … This is very valuable to us, and we will pay."

The task force made up of FBI and Pima County detectives continues to investigate her kidnapping and search for Guthrie and her abductors.

Editor's note: The video featured on this page was recorded on May 12.