TMZ has received a 4th email from the man claiming to know who kidnapped Nancy Guthrie and where she is ... and we have a proposition for that person.

NANCY GUTHRIE COPS ‘PROBE BOTCHED ROBBERY’SAVANNAH GUTHRIE MAKES NEW PLEASAVANNAH GUTHRIE PLEADS 'DO THE RIGHT THING'SHERIFF RULES OUT BURGLARY GONE BADSHERIFF REVEALS SMOKING GUN...DEFENDS SHAMBOLIC INVESTIGATIONSUSPECT SHOPS AT WALMARTDNA MATCHES