Article continues below advertisementThe search for Nancy Guthrie, the 84-year-old mother of Savannah Guthrie, continues as the case enters its fifth week. Now, a former FBI agent is pointing to a troubling detail that may have left Nancy especially exposed the night she disappeared.During a Sunday, March 8, episode of "Brian Entin Investigates," reporter Brian Entin spoke with former FBI special agents Maureen O'Connell and Jim Clemente about the ongoing mystery.