Nancy Guthrie‘s kidnapper has eluded authorities for 2 weeks, but the ransom note TMZ received is of intense interest to the FBI, and Harvey Levin and Mark Geragos both agree … it may be the key to cracking the case.

H&M’s latest “2 Angry Men” podcast makes it clear … the FBI is laser focused on that ransom letter, for reasons we cannot publicly discuss. They are also interested in the man who has sent TMZ 3 demand emails asking for bitcoin in return for giving up the kidnapper’s name. BTW … the man says the kidnapper is the “main individual” — meaning there’s more than one person involved.

Law enforcement’s dramatic move Friday night apparently did not yield results, but there are a number of clues, including unknown DNA found in Nancy’s house. It’s currently being analyzed.

TMZ has identified the backpack and the jacket the kidnapper was wearing … we believe it to be an Athletic Works Fusion Knit Jacket — law enforcement has not confirmed.  Both items are sold at Walmart, so they may help law enforcement track down the kidnapper.