Authorities are in their third week of searching for the 84-year-old mother of ‘Today’ co-host Savannah Guthrie. Nancy was last seen on Jan. 31 at her Tucson, Ariz. home.

The FBI is in contact with authorities in Mexico as the search for Nancy Guthrie continues, law enforcement sources told ABC7, NBC News and CBS News.

The Pima County Sheriff’s Department and FBI are in their third week of searching for the 84-year-old mother of Today co-host Savannah Guthrie. Authorities believe Nancy was kidnapped from her Tucson, Ariz., home in the middle of the night on Feb. 1.

The FBI declined to comment when reached by PEOPLE. However, Tracy Walder, a former CIA and FBI agent, shared more about how the FBI works with Mexican authorities.

“The FBI contacts its Legal Attaché (Legat) offices worldwide primarily through the International Operations Division (IOD) at FBI Headquarters in Washington, D.C.,” she told PEOPLE. “I really can’t say if it’s standard practice or common. It really just depends if they think they have crossed the border.”

Nathan Congleton/NBCU Photo Bank/NBCUniversal via Getty

Two law enforcement officials told NBC News there’s no evidence Nancy was taken across the U.S.-Mexico border.

In a press statement previously obtained by PEOPLE, the Pima County Sheriff’s Department did not elaborate further.

“PCSD has received various requests for confirmation of various topics including working with Mexican authorities, utilizing polygraph tests, specific video surveillance requests, financial analysis, etc. PCSD is not confirming or releasing any details regarding those topics at this time,” the statement reads.

Last week, the FBI released surveillance photos and video of a masked, armed suspect appearing to tamper with a camera at Nancy’s front door on the morning of her purported kidnapping.

That person has yet to be identified, but is described by the FBI as a “male, approximately 5’9” – 5’10” tall, with an average build.” In the video, the person is wearing a “black, 25-liter ‘Ozark Trail Hiker Pack’ backpack,” according to a post on X.

The suspect seen in security footage; Nancy Guthrie.FBI Phoenix/X; Savannah Guthrie/Instagram

Authorities have said they are looking into multiple leads. The Pima County Sheriff’s Department announced Tuesday, Feb. 17 that DNA evidence left behind on gloves found about two miles from Nancy’s home did not yield any matches when law enforcement ran the profile through the national DNA database.

The department also said in a press statement that they are “looking into additional investigative genetic genealogy options for DNA evidence to check for matches.” They added that other DNA found at the property “is being analyzed and further testing needs to be done as part of the investigation.”

Pima County Sheriff Chris Nanos previously said investigators are working with Walmart locations across Arizona to track down the suspect’s clothing and backpack. As for the FBI, they are visiting local gun shops, inquiring about past customers and purchases.

Additionally, law enforcement sources told CBS News they are using a “signal sniffer” in an attempt to detect signals from Nancy’s pacemaker.

“It’s been two weeks since our mom was taken,” she said in a clip shared on Sunday, Feb. 15. “And I just wanted to come on and say that we still have hope. And we still believe.”

Nanos ruled out Nancy’s family and siblings as potential suspects on Monday, Feb. 16.

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A $100,000 reward has been offered by the FBI for any information leading to Nancy’s recovery or an arrest in the case. On Wednesday, Feb. 18, that reward doubled after the PCSD received an anonymous donation.

Anyone with information about Nancy’s disappearance is asked to please contact 1-800-CALL-FBI (1-800-225-5324) or the Pima County Sheriff’s Department 520-351-4900.