A retired police sergeant from Phoenix, Arizona — just a two-hour drive from where Nancy Guthrie lives in Tucson — says there are plenty of fresh clues to dissect in the newly-released images from her Nest doorbell camera. “Overall, it’s a huge break in the case,” Troy Hillman, a retired cold case homicide sergeant with Phoenix Police Department, exclusively tells Us Weekly as the search for 84-year-old Guthrie continues. The FBI has released six black-and-white photos and three video clips showing a potential subject involved, who was wearing a mask, black gloves and a backpack when approaching Guthrie’s residence on…