Pima County Sheriff, Chris Nanos has been regularly criticized over his handling of the Nancy Guthrie case(Image: Jan Sonnenmair, Getty Images)

Pima County Sheriff Chris Nanos has faced criticism for what's been described as a "highly unusual" approach as the investigation into Nancy Guthrie's disappearance continues.

The 84-year-old mother of Today Show host Savannah Guthrie wasabducted from her Tucson, Arizona, residenceovernight between January 31 and February 1. She remains missing.

Whilst the Sheriff's Department and the FBI have been leading the investigation, it has now emerged that the sheriff has allegedly "locked down" the probe, restricting decision-making authority to himself and two of his senior detectives. This development follows revelations from a former FBI agent about a hiddencodeword that Savannah used in her message to the kidnappers.

Multiple PCSD sources speaking to the Daily Mail have claimed that three decision makers are directing the department's investigation - Sheriff Nanos, Chief Jesus Lopez and Captain Juan Carlos Navarro.

Nancy Guthrie has been missing for three weeks(Image: Savannah Guthrie/Instagram)

One law enforcement source claimed that the sheriff "will only let himself or two of his handpicked staffers make decisions on the case."

They added: "Everybody else is being told what to do, no one else has a say so or an opinion. It's just three men making the decisions."

According to the insider, the move is "incredibly unusual" particularly given the investigation's large scale and FBI involvement.

"It's limited to the thought processes of three men. They're keeping everything from the FBI - they just aren't sharing," the source claimed. Another source who spoke to the publication described it as "highly unusual" that only command staff is leading the investigation, noting, "Normally an experienced detective would steer it and provide updates through the chain of command."

Source: Drudge Report