New Delhi, Aug. 4 -- The investigation into the disappearance and presumed death of Nancy Guthrie, the 84-year-old mother of NBC "Today" co-host Savannah Guthrie, should be handed over to the FBI after six months without a breakthrough, according to sources who spoke to Page Six.

Page Six reported that people are "shocked and disturbed" that authorities have made no significant progress since Nancy Guthrie was allegedly abducted from her bed at her Catalina Foothills home near Tucson, Arizona, on February 1.

"There's a killer on the loose. They need to focus their resources on finding that person rather than bickering," one source told Page Six, criticizing what they described as infighting between law enforcement agencies.

Retired FBI...