New Delhi, May 14 -- The investigation into the disappearance of Nancy Guthrie, the 84-year-old mother of Savannah Guthrie, remains active 100 days after she vanished from her Arizona home, with local authorities and the FBI continuing to pursue DNA, digital and forensic leads.

Speaking to local station KOLD-TV, Pima County Sheriff Chris Nanos said investigators believe they are making progress in the case despite growing public frustration over the lack of arrests.

"They are working hard to get this resolved, and I think every day they get closer," Nanos said in the interview published on May 12.

Nancy Guthrie was last seen on January 31 in her Catalina Foothills neighbourhood north of Tucson, Arizona, before what investigators believ...