Finally, an arrest in the Nancy Guthrie kidnapping, but it’s not one of her captors … it’s a guy the feds claim sent text messages to Nancy’s family asking them about bitcoin … and the FBI says they don’t believe the guy has any connection to the ransom note.

According to new legal docs, obtained by TMZ, the feds say a Los Angeles man named Derrick Callella texted Nancy’s daughter Annie and her son-in-law Tommaso Cioni, “Did you get the bitcoin were [sic] waiting on our end for the transaction.”

The FBI says the texts were sent Wednesday, shortly after ‘TODAY’ anchor Savannah Guthrie uploaded a video of her siblings making a plea to Nancy’s captors. In the video, Savannah mentioned the ransom note, begged for proof of life and said they were ready to talk.

TMZ was sent a ransom note on Tuesday that demanded millions of dollars in bitcoin in exchange for Nancy’s safe return and set two deadlines … we forwarded the note to law enforcement and now the FBI is divulging certain details from the note.

To be clear … in the criminal complaint against Callella, the FBI says the text messages he allegedly sent Nancy’s family have NOT been linked to the ransom demand.

The feds say Callella used a virtual phone number to send the text messages … the FBI says the number he used was registered to an email account using his first and last name, and records indicated the virtual phone number was accessed from an IP address associated with his California residence.

Callella, according to the FBI, admitted to sending the two text messages and told investigators he pulled family information from a cyber website and had been following the Guthrie kidnapping in the media.

The feds say Callella told them he sent the texts to see if the family would respond … and the FBI says data shows that he also called a Guthrie family member 3 minutes after sending the texts and that the call lasted 9 seconds.