India, Feb. 10 -- The law enforcement has intensified its investigation into the disappearance of 84-year-old Nancy Guthrie, mother of NBC's Savannah Guthrie. They were seen searching a septic tank behind her Arizona home on Sunday.

Nancy Guthrie was last seen in the early hours of January 31 at her Tucson residence after being dropped off by her daughter and son-in-law.

When she did not show up for church the following morning, her family reported her missing, triggering a search that has drawn national attention.

In the most recent development of the Nancy Guthrie kidnapping case, FBI agents and Pima County Sheriff's Department detectives were seen probing the septic tank.

They gained entry to the backyard manhole and used long pole...