TMZ reported receiving a "highly sophisticated" ransom note as the search for Nancy Guthrie expands internationally to Mexico. The FBI has reportedly expanded its search south of the U.S. border and asked law enforcement officials in Mexico to join the search for 84-year-old Guthrie, the mother of "Today" show co-host Savannah Guthrie, who went missing three weeks ago from her Tucson home. Sources told TMZ they believe Guthrie could have been taken across the border, but it's unlikely it happened immediately after she was taken from her home. Authorities have released video and images of a suspect who was at her home overnight between Jan. 31 and Feb. 1, when investigators believe Guthrie was kidnapped. TMZ has received multiple ransom notes over the last several weeks. It's unclear if they were authenticated by law enforcement. "TMZ has obtained another ransom note -- this one a highly sophisticated demand involving a cryptocurrency other than bitcoin. The email demands a dollar amount similar to the $6 million ransom demand in the previous email we received, days after the kidnapping. This email graphically describes the consequences if the ransom isn't paid," TMZ reported."The new ransom demand email includes a crypto account number different from the original. We have forwarded the email on to the FBI and will not be more specific," the outlet reported.