DNA that doesn't belong to the 84-year-old or anyone close to her was obtained from her property and is being tested, according to the sheriff.

It’s been 16 days since Nancy Guthrie was reported missing, and investigators working the case that has captivated the nation’s attention are encountering a unique mix of challenges.

Nancy Guthrie, the 84-year-old mother of "TODAY" co-anchor Savannah Guthrie was last seen Jan. 31 when she was dropped off at her home in the Tucson, Arizona.

Pima County Sheriff Chris Nanos told CBS News the suspect's backpack is one of the most promising leads in the case, as the search continues for Nancy Guthrie.

• Glove analysis: A glove found near Nancy Guthrie’s home appears to match the one worn by a suspect seen in her home’s doorbell camera footage, according to the FBI. DNA from the glove is being analyzed in an attempt to identify a suspect as the search stretches into a third week .

The race against time intensifies for missing 84-year-old Nancy Guthrie as investigators rush DNA processing while she remains without vital medication.

Nancy — the mother of 'Today' show co-host Savannah Guthrie — was reported missing on Feb. 1

The search for missing 84-year-old Nancy Guthrie, mother of “Today” show host Savannah Guthrie, has stretched into a third, anguished week, with mounting pressure on investigators and a family grappling with uncertainty.