India, May 10 -- A desert "wash" just a couple of miles from Nancy Guthrie's Tucson home is posing a major challenge for investigators probing the case, Dave Smith, a retired lieutenant with the Arizona Department of Public Safety and a law enforcement consultant, told Fox News Digital. The expanse is a natural drainage ditch, thick with brush so dense that people can hardly see the surrounding homes, many of which cost seven figures.

The terrain, carved through the city and the rest of Pima County, is typical of the region.

"The whole Tucson Valley is literally built around these arroyos, these ephemeral rivers," Smith said. "This is literally your green belt here, only instead of parks and things like the rest of the nation has, we ha...