Investigators searching for Nancy Guthrie, the 84-year-old mother ofTodaypresenter Savannah Guthrie, say they are examining biological evidence and continuing to pursue thousands of public tips as the case approaches three weeks since she was last seen in Arizona.​​

Authorities in Pima County have treated the Catalina Foothills disappearance as asuspected abduction, and police have warned that cross-checking tips and evidence is likely to be a lengthy process even as pressure grows for a breakthrough.​​

Mexico's Secretary of Security, Omar García Harfuch, told reporters that there is "no indication, nor any line of investigation that would suggest" Nancy Guthrie was in Mexico.https://t.co/RQbHQ7QHUE

Pima County Sheriff Chris Nanos told KGUN that investigators are working with biological evidence recovered at the home Nancy Guthrie disappeared from, though the department has not publicly detailed what that evidence shows. KGUN reported the sheriff's office and the FBI have been 'flooded' with information from the public and that deputies have turned to software to help sort and prioritise leads.​

The sheriff's department has received '18 thousand tips and counting,' KGUN said, with Nanos explaining that detectives focus first on what he described as the 'hottest tips.' 'Here's a level one tip—-that video—-the doorbell,' Nanos said, adding that another high-priority lead might involve identifying a backpack seen in footage.​

DNA on glove found near Nancy Guthrie's home returned no matches in federal database, sheriff's department sayshttps://t.co/x6A27xP2tApic.twitter.com/V8ETdCJcqP

Nanos urged the public to keep coming forward, arguing the flow of information matters as investigations move into later stages. 'Because let's face it, you've been around enough to know that when these tips dry up this case goes cold. We believe somebody out there knows who did this. We need that person to call,' he said.​

CBS News reported that, on Feb. 13, the sheriff's department said DNA that did not belong to Nancy Guthrie or people in close contact with her had been collected from her residence, with investigators working to identify who it belongs to. The department did not disclose where on the property the DNA was found, CBS News said.

Nancy Guthrie was last seen on Jan. 31 and reported missing on Feb. 1 after she did not attend church, according to CNN and statements from local authorities. CBS News said investigators believe she was abducted from her home during the night.​

The FBI has circulated images from doorbell-camera video from the night she is believed to have been taken, and CBS News reported the footage showed a person wearing a ski mask, gloves and a backpack. The FBI described the suspect as a male of average build with an approximate height of 5ft 9in to 5ft 10in, CBS News reported.

Source: International Business Times UK