A device to detect emissions from Nancy Guthrie‘s pacemaker is among the tools investigators are using as their search for her continues into its third week, law enforcement sources told CBS News. 

The high-tech tracking tool, called a “signal sniffer,” has been mounted on a helicopter and may help detectives pinpoint her location, the sources said. Signal sniffers are often used in missing person cases because they can detect low-power electronic signals, such as those emitted by a pacemaker.

According to the sources, the helicopter carrying the device is flying slowly and at a low altitude over the area where investigators are still hoping to find Guthrie.

The 84-year-old mother of “Today” show co-host Savannah Guthrie was reported missing when she failed to show up for church on Feb. 1, after vanishing in the middle of the night from her home in Tucson, Arizona, apparently in an abduction. 

Her family has issued multiple public pleas for Guthrie’s safe return. The FBI recently released a description of a male suspect wanted in connection with her disappearance, who federal authorities say is roughly 5 feet 9 inches or 5 feet 10 inches tall with an average build. 

In chilling footage from the Nest doorbell at Guthrie’s home, the man was seen wearing a black 25-liter Ozark Trail Hiker Pack backpack, the FBI said. Sheriff Chris Nanos, of Pima County, Arizona, told CBS News that the backpack was sold exclusively at Walmart and called it one of the most promising leads in the case so far. 

He said investigators were still working to identify each brand of apparel worn by the suspect in that doorbell footage, but they believe his clothing and face mask were purchased at Walmart, too. 

A black glove found near Guthrie’s home, which the FBI said “appears to match the gloves the subject in the surveillance video,” has also undergone DNA testing. Federal authorities said they received the preliminary result of those tests on Saturday, and, once confirmed, the findings would be entered into an “unknown male profile” in the FBI’s national database for DNA samples. The database stores DNA profiles for people with criminal histories and can be a valuable tool to match unknown samples to identifiable ones.

Not much else in the way of forensic evidence has led investigators to a suspect, Nanos said, although they have collected other DNA samples from Guthrie’s property. 

The FBI doubled its reward last week to $100,000 for tips leading to Guthrie’s location or the arrest and conviction of anyone involved in her disappearance. Authorities said they have received two emails throughout the course of the investigation so far that they are taking seriously, including one that appeared to be a ransom note and demanded payment in bitcoin.

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