How Walmart and Google became key to the search for Nancy Guthrie

Walmart and Google have been assisting law enforcement in the disappearance of Nancy Guthrie.Brandon Bell/Getty Images; Jeremy Moeller/Getty ImagesGoogle and Walmart have been assisting authorities in the disappearance of Nancy Guthrie.Investigators recovered footage from the woman's Nest doorbell camera with Google's help.Walmart is tracking backpack purchases linked to the case.In the search for Nancy Guthrie, authorities have relied not only on traditional investigative work but also on data