Article continues below advertisementNearly one month after Nancy Guthrie vanished from her Tucson, Ariz., home, questions are mounting about whether federal authorities could soon take primary control of the investigation.The 84-year-old mother of Today co-anchor Savannah Guthrie was last seen on the night of January 31.Article continues below advertisementFormer Agents Weigh InSource: @savannahguthrie/InstagramNancy Guthrie has been missing since January 31 after a masked suspect was caught on camera outside her Tucson home.