Nancy Guthrie Cold Case Letter Claims She Was with Kidnappers in Mexico

There are a couple of new notes in the Nancy Guthrie cold case ... both from the same person offering information on the kidnapper, but for the first time they're revealing an exact location and claiming they saw her in Mexico.

TMZ received the first new note Monday morning -- the same day Savannah Guthrie made her return to "TODAY" -- and it's from the person who has been offering to rat out the kidnappers for nearly two months now. They say their demand for 1 bitcoin to "deliver them on a silver platter" still stands.

Shortly after we talked about the first note on "TMZ Live," the person sent a second letter saying ... "I Saw her alive with them in the state of Sonora Mexico."

Sonora is a large Mexican state bordering Arizona and parts of New Mexico. Nancy was abducted from her home in Tucson, AZ, about 70 miles from the border on Feb. 1.

However, the sender is not suggesting Nancy is still alive ... in the first note, they say, "she is dead."

We sent the first note to the FBI, but it seems the feds aren't convinced it's legit, at least, based on the fact there's been no deposit into the related bitcoin address ... the same account they created back in February.

The person who sent the notes clearly senses the FBI's disbelief ... has that same sense, because the first letter says ... "It's unbelievable that millions have been wasted and yet here I am willing to deliver them on a silver platter since the 11th of february for a bitcoin but I am disregarded as a scam ... they are free and the case is frozen but the ego's remain hot when it comes to me. Arrogance at it's finest."

Bitcoin's price has been dropping, so it's interesting Nancy and the FBI aren't even taking a flier here ... the person says they will give up the info for half a bitcoin, and then when there is a public arrest, the other half gets transferred to their bitcoin wallet.

They also try to distance themselves from Nancy's kidnapping, claiming they've been out of the U.S. for more than 5 years, and had nothing to do with the "horrific crime."